THE UNIVERSITY OF TEXAS PUBLICATION NUMBER 6005 MARCH 1, 1960 Graptolite Faunas of the Marathon Region, West Texas WILLIAM B. N. BERRY BUREAU OF ECONOMIC GEOLOGY THE UNIVERSITY OF TEXAS, AUSTIN JOHN T. LONSDALE, Director Publications ofThe University ofTexas COMMITTEE ON PUBLICATIONS J. T. LONSDALE L. LEBOWITZ L. F. ANDERSON H.T.ODUM R. F. DAWSON H.J. OTTO J. R. D. EDDY w. P. STEWART H. HELSON J. R. STOCKTON F. H. WARDLAW ADMINISTRATIVE PUBLICATIONS AND GENERAL RULES w. B. SHIPP c. H. EADS J. G. AsHBURNE w. J. HANDY R. LEVY The University publishes bulletins twice a month, so numbered that the first two digits of the number show the year of issue and the last two the position in the yearly series. (For example, No. 6001 is the first publication of the year 1960.) These bulletins comprise the official publications of the University, publications on humanistic and scientific subjects, and bulletins issued from time to time by various divisions of the University. 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LONSDALE, Director The benefits of education and of useful knowledge, generally diffused through a community, are essential to the preserva­tion of a free government. SAM HOUSTON Cultivated mind is the guardian genius of Democracy, and while guided and controlled by virtue, the noblest attribute of man. It is the only dictator that freemen acknowledge, and the only security which freemen desire. MIRABEAU B. LAMAR PUBLISHED BY THE UNIVERSITY TWICE A MONTH. ENTERED AS SECOND-CLASS MATTER ON MARCH I2, I9I3, AT THE POST OFFICE AT AUSTIN, TEXAS, UNDER THE ACT OF AUGUST 24, I9I2 Contents PAGE Abstract ···-·····---------------------------------------------------------------······-···-··-··---------------------··-····--·· 1 Introduction ·····-·····-------------------------------------------------·--·--·----··--·····-----------------------····-···· 1 Scope of the study ·-·-·-----··--------------------------------------------------------------···-----------------1 Acknowledgments ---------------------------------·--··----·········-············--········-······-···----······-2 Previous work ····--······----·-··-················ -····················-------··-·-·······-···-----·-···· ·----·-··· 2 Stratigraphy ····--·----·-----·············-······-·----·-----·----···-·-···----···-······-··-····-------·-···-----·---······ 4 Cambrian system ·-----·---------·-------------··--·-··---····--····-··-·······-----·----······-·-····--········-4 Dagger Flat sandstone ·--------------------·-·---···-····-····-----------------·---····-···----··-----4 Stratigraphy --···········-·-·····-···· ·------·------···--················-----·-----·--·······----·· 4 Fossils and age ··-·--··---···-·-··········---------·---·-·-----··-----------------------------····· 5 Ordovician system ·--··------·----·----···---·----····---------···----------··-···············----··-----·-····· 5 General features ·------------------------·---------····--····-·-·····------------------···--········------5 Graptolite zones -------------------·----------··---------·····---··-··············-------········--··-----7 Marathon limestone ·········---------------··--·--·----···-·····-···········----------·----···--······-8 General features ------------------------------------------·--····--·······-··----------·----······ 8 Local features ---------------···---------------------··----··-·-······ -··----··············-----·--· 10 Marathon anticlinorium --····--··-----··-······----···-···---------····-··········--· 10 Dagger Flat anticlinorium -----··--------·-··--·--·---···········-··-·--------------14 Old Jones ranch and Solitario areas ···---···--····-········-··---------------15 Fossils and age ··---·-·---·-----···-···-·-······--····-············--·····-····-····----------·----15 Alsate shale ········· ----··---··-------------·----··--······-···············----·····------------------------· 19 General features -····-----··--·-··-···········---····---···-·····---···----···--····-······-------19 Local features ···-·····--····-·--···--·-··---···--····-·-············--··-······---··----········-·· 19 Marathon anticlinorium ·····-····---·····-·····-····---····--····-··················· 19 Dagger Flat anticlinorium ----···--····--·-··--····-··-··-······-·····---···----···-20 Fossils and age ··-·················-·-···----········--·····--·-··--····-··--··-·····----··----···· 20 Rodriquez Tank sandstone ···-······--·--------------·-·-······--··--·--·-----·---·-··----------···· 20 Fort Pena formation·--······----------------------------·-----------··---···----·------------------··--20 General features ----------·········-·-···········-···-·-····-··------··----······················-20 Local features ··················-·····································-···········--·····--··-------21 Marathon anticlinorium ----··----··----···-·····---····--····--····------------------21 Dagger Flat anticlinorium ····················-·······-------·-······-············--21 Old Jones ranch and Solitario areas ···---···---················----··-----··---21 Fossils and age ----·-----------·------------------------------------··-----··----·····-·····-····--21 Woods Hollow shale---····--····---···----····---··----··--·-··-·-····--···········--······---------··· 23 General features ------------------------------------------·----------·-----------······--····---·· 23 Local features ························-······--····-----·-----·--·················------············ 24 Woods Hollow Mountains ·---·-----··-·········--·-·-----------····-······--·------24 Other localities ··-·-···········-·····--······-····-·····--·--·--·····-··-··----············ 24 Bureau of Economic Geology, The University of Texas Fossils and age -----------·-------··-··----··-····---··-·-··-·····---------------------------------24 Maravillas chert ---------------·--------··---------------------·-----------·-----·---·-·------------------27 General features ----··----··-·-··----··--··-·----··----------·-·---··----······---------·-·-··--·-27 Local features ------·----·----······---··--·-·-·-·--·--··----·----·-·--·--··----··-----·--··--··--·· 27 Marathon anticlinorium ·-·····-····----·--·-·----------------··-----------··---------27 Dagger Flat anticlinorium ·---··----------------·-----------··------·--·------------28 Southern exposures -----·---·-------------·----·---------------------------··-----·---·--28 Fossils and age -----·----------·----------------------·-------------·----··-----------·-----------· 28 Depositional history of the Ordovician strata --------------------------------------------32 Devonian system -----·-----------------·----------------------------·------------·-----·-------·------------------34 Correlation -----------------------------------------------------------------·------------------------------------------------35 Correlation within North America --------------------------------------------------------------------35 Intercontinental correlation -----------------------------------·--------------------------------------------38 Systematic paleontology ----------------------------------------------------------------------------------------------45 Class Graptolithina -----------------------------------------------·-----·----------------------------------------45 Order Dendroidea --------------------------------------------------------------------------------------45 Family Dendrograptidae -------------------------------·------------------------------------45 Family Anisograptidae ------------------------·-----------------------------------------------45 Family Ptilograptidae ------------------------------------------------------------------------49 Order Graptoloidea ------------------------------------------------------------------------------------49 Family Dichograptidae ----------------------------------------------------------------------49 Family Corynoididae --------------------------------------------------------------------------68 Family Cryptograptidae -------·--------------------------------------------------------------69 Family Leptograptidae -------------------------------------------------------------·----------72 Family Dicranograptidae --------------------------------------------------------------------73 Family Diplograptidae ------------------------------------------------------------------------78 Family ?Diplograptidae ----------------------------------------------------------------------94 Family Lasiograptidae ------------------------------------------------------------------------94 Family Retiolitidae ---·--------------------------------------------------------------------------96 Bibliography -------------------------------------------------------------·--------------------------------------------------98 Appendix ----------------------------------------------------------------------------------------------------------------------105 I. Measured sections ----------------------------------------------------------------------------------------105 II. Collecting localities --·----------------------------------------------------------------------------------· 120 Index -----------------------·------------------------------------------·---------------------------------------------------------167 Illustrations FIGURES-- PAGE 1. Index map showing the Marathon region ------------------------------------------------------3 2. Map of south-central United States showing areas of Ordovician exposures 6 3. Diagram showing graptolite zones with sketches of the principal species in each --------------------------------------------------------------------------------------------------------------9 PLATES-­ I. Index map showing position of measured sections and collecting localities ----------------------------------------------------------------------------------------------------In pocket 2. A, Limestone chip conglomerate lens in the Marathon limestone. B, Alsate shale at its type locality on Alsate Creek ----------------------------------------11 3. A, Anticlinal valley in the Woods Hollow shale on the crest of Simpson Springs Mountain. B, Typical exposure of the Maravillas cherL---12 4-20. Fauna of graptolite zones 1-15 --------------------------------------------------------------131-165 Tables TABLES-­ I. Relation of nomenclature applied to Cambrian and Ordovician rocks in the Marathon region ----------------------------------------------------------------------------------13 2. Correlation of graptolite-bearing sequences in North America --------------------36 3. Correlation of Ordovician sequences in the United States (Marathon area), Australia (Victoria), and the British Isles based on graptolite zones 39 Graptolite Faunas of the Marathon Region, West Texas WILLIAM B. N. BERRY1 ABSTRACT In the Marathon region, graptolites have been found throughout a 2,000-foot sec­tion of limestones and shales from the base to the top of the Ordovician system. This is the most complete sequence of Ordo­vician graptolites known in North Amer­ica. Fifteen fauna! zones are recognized. This region will provide a standard sec­tion against which other graptolite-bear­ing formations may be compared. Other graptolite-bearing formations in North America are correlated with the Marathon zones. Further, the Marathon zones are correlated with the British and Australian Ordovician graptolite zonal suc­cessions. The zonal assemblages in the Marathon region for the Lower and lower part of the Middle Ordovician are similar to the Australian but differ from the Brit­ish. The upper part of the Middle Ordo­vician and the Upper Ordovician assem­blages are nearly identical in all three tonal sequences. The report includes an extension of de­tailed stratigraphic study to lesser-known areas southeast and southwest from the Marathon basin. P. B. King mapped the basin in detail and recognized five Ordo­vician formations. From oldest to young­est these are the Marathon limestone, AI­sate shale, Fort Pefia formation, Woods Hollow shale, and Maravillas chert. The boundaries of the Marathon limestone and Alsate shale are modified from King's (1937) usage. Also, a progressive change to a more arenaceous nature southward from the basin is noted for the lower part of the section, and a new formation, the Rodriquez Tank sandstone, is recognized in the southern exposures. The stratigraphic position of every spe­cies of graptolite found in the Marathon region is correlated with occurrences of these species elsewhere in North America and in England and Australia. Seven new species of graptolites are described. INTRODUCTION SCOPE OF THE STUDY The Ordovician rocks in the Marathon basin have long been a subject of consider­able interest, and since publication of King's (1937) Professional Paper on the area, they have been under study by per­sonnel of oil companies, summer field camps, and field conferences. Graptolites have been known from the sequence for over 50 years, and Udden, Baker, Bowman, and King all made collections from it. However, no systematic study of the fauna has been made. Furthermore, exposures of Ordovician rocks southeast and south­west of the basin have never been ade­quately described. The present work is a detailed stratigraphic and paleontologic study of the Ordovician strata and fauna in the entire Marathon region. The field work was carried out during the summers of 1954 and 1955, and the laboratory work was done at Yale Univer­sity during the academic year 1955-1956 and at Harvard University during the sum­mer of 1956. The area studied includes the Marathon basin and the old Jones ranch (now Slaughter ranch), Persimmon Gap, Rough Creek, and Solitario localities as shown on the index map (fig. 1). King's geologic maps were used as a base and l Vi1iting Atsielant Profe11or of Paleontology, University of California. Berkeley. Bureau of Economic Geology, The University of Texas attention was concentrated on making as many collections of fossils as possible that were accurately located stratigraphically. The major portion of the collections is at Yale Peabody Museum. The types of new species and nearly all of the figured specimens are deposited there and have Yale Peabody Museum (YPM) catalogue numbers as indicated on the plate cap· tions. Smaller, but representative, collec­tions have been given to Professor H. B. Whittington at the Museum of Compara­tive Zoology at Harvard University, and to Professor 0. M. B. Bulman at the Sedg­wick Museum at Cambridge University. ACKNOWLEDGMENTS The writer is indebted to Professor Whit­tington for suggesting this project and for continued encouragement and guidance. Professor C. 0. Dunbar supervised much of the research and critically read the manuscript. Dr. J. L. Wilson visited the writer in the field and gave valuable suggestions on all phases of the work. Professor J. E. Sanders discussed certain vexing problems and made valuable criticisms. The writer is also indebted to Professor Bulman for checking the iden­tifications of a representative collection of graptolites and for comments on the inter­continental correlations. The writer expres· ses grateful thanks to: Dr. C. E. Decker for permitting examination of the collec­tions at the University of Oklahoma and for discussing correlations; Dr. William Ham for advising on the correlation of the Arbuckle sequence with the Marathon; Professor R. W. Harris and Mr. M. E. Upson for aiding in the identification of the ostracods and discussing the corre­lation of the Arbuckle and Marathon suc­cessions; Professors Paul Fan, J. P. Brand, and Richard Rush for suggesting collecting localities and discussing the stratigraphy; Dr. William Pitt for spend­ing several days guiding him through the Ouachita Mountains; Mr. H. M. Nielson and Dr. W. Hess for making the facilities of the Gulf Oil Corporation field party available and for discussing the stratig­ raphy in the field; Mr. Clinton Kilfoyle for making available for study Dr. Ruede­mann's collections at the New York State Museum in Albany, New York; and Dr. G. Arthur Cooper for permitting the study of the Marathon region graptolite collec­tions at the U. S. National Museum. The writer was ably assisted in the field by David B. Clarke during the first sum­mer and by Martin D. Collins, Jr., during the second. The large collections would not have been possible without their enthusi­astic aid. This project was made possible by a Broderick Fund grant from the Depart­ment of Geology at Harvard University to cover the expenses of the first summer, and by a research grant from Shell Research and Development Company for the com­pletion of the work. It was presented as a dissertation for the degree of Doctor of Philosophy at Yale University in May 1957. PREVIOUS WORK R. T. Hill in 1900 gave the first brief summary of pre-Carboniferous rocks in the Marathon region. He noted "closely folded Paleozoic limestone, shales and cherts, probably of lower Helderberg age." Udden (1907) traveled across the Marathon basin during the course of his investigation of the geology of the Chisos country and de­scribed the highly folded and faulted dark shales, limestone, and cherts. He collected some fossil fragments from ledges of bi­tuminous limestone exposed "along the wagon road near Ridge Spring and at dif· ferent points south from this place for a distance of ten miles." The fossils were sent to Charles Schuchert, who identified Tri­nucleus, Plectambonites, Rafinesquina, and a possible Zygospira (Udden, 1907). Dr. Schuchert considered the fossils to be of Trenton age. The first comprehensive stratigraphic work in the area was that of Baker and Bowman (1917), who in 1915 collected fossils and made brief studies of the pre­Carboniferous succession. E. 0. Ulrich studied the fossils and recognized six dis­ Graptolite Faunas, Marathon Region tinctive faunas in the collections. Baker and Bowman divided the pre·Carbonifer· ous section into four formations on the basis of the fossil determinations and the lithology. In 1929 and 1930, P. B. King made a regional study of the entire Marathon area and mapped two quadrangles in detail. He restudied the Ordovician rocks carefully, measuring seventeen sections and making fossil collections. A small part of the fauna collected was studied by Kirk, Ulrich, and Ruedemann. King (1931, 1937) divided the Ordovician section into five formations and described the rocks in detail. His now classic "Geology of the Marathon region, Texas," remains as the standard work on the geology of this region and has formed the basis from which road logs and articles have been written for several field trip guidebooks of the West Texas Geological Society (Maxwell et al., 1941, 1949; Adams et al., 1952; Lonsdale et al., 1955). Recently, Wilson (1954a, 1956) de­scribed trilobite faunas from the Upper Cambrian-Lower Ordovician beds of the Dagger Flat and Marathon formations and from exotic boulders of the same age near the top of the Middle Ordovician Woods Hollow shale. Wilson (1954b) ex­tended the pre-Carboniferous stratigraphy described by King for the Marathon basin proper to less known outcrops in the Soli­tario, Persimmon Gap, and old Jones ranch area which lie respectively southwest, south, and southwest from the well-known basin. STRATIGRAPHY CAMBRIAN SYSTEM DAGGER FLAT SANDSTONE Stratigraphy The oldest rocks exposed in the Mara­thon region are the sandstones, shales, and limestones of Late Cambrian age named Dagger Flat sandstone by King (1931, p. 1064) from exposures in the Dagger Flat, 13 miles south of the town of Marathon. The greatest area of exposure of these rocks is on the south side of the Dagger Flat­northeast of the Buttrill ranch-where the massive sandstones form conspicuous ledges, hut the formation is also exposed in the core of the Marathon anticlinorium. The base of the formation is not exposed, hut the Turner No. 1 Combs, 16 miles south of Marathon, located on the north­west flank of Threemile Hill on beds below the top of the formation, was drille? through approximately 200 feet of the typi­cal Dagger Flat sandstone, then through a considerable thickness of black shale. No fossils were obtained from the shale. The bore hole was presumed to he parallel to the dip of the beds near the bottom of the hole and the actual thickness of shale penetrat~d is unknown. Because the main Threemile Hill thrust fault is 100 to 200 yards south of the well location a?d seve~al subsidiary thrust plates are associated with it the contact between the sandstone and shale may he the trace of one of the faults. The Dagger Flat sandstone was first de­scribed by Baker and Bowman in a section on Threemile Hill and was designated, without age assignment, as Member 2 of their "Marathon series." King ( 1937) de­scribed the formation in detail in its four principal areas of outcrop-Dagger Flat, Threemile Hill, Woods Hollow Tank,_ and the Marathon anticlinorium. Wilson (1954a) restudied the formation and di­vided it into two members-a lower, But­trill Ranch member, and an upper, Roberts Ranch, member. . The Buttrill Ranch member, which crops out in the Dagger Flat anticlinorium only, is best exposed about 5 miles northeast of the Buttrill ranch house and is typically a "'raywacke-shale sequence. Wilson ( l 954a) ~easured 270 feet of the member at its type locality. No fossils have yet been found in it. The Roberts Ranch member was pro­posed by Wilson (1954a) for the higher beds of the Dagger Flat sandstone exposed along the crest of the Marathon anticli­norium, which is traversed by the road to Roberts ranch. It is principally black shale hut does include beds of sandy,fine-grained dark gray limestone and brown graywacke. Its best exposures are 4 miles southwest of Marathon where a 225-foot section is ex­posed. Wilson (1954a, p. 251) designated the Roberts Ranch member in both its out­crop belts as "lying below prominent lime­stone pebble conglomerates interhedded with dark shale." The writer with Wilson visited sections in the Marathon anticli­norium and found Tremadoc graptolites in beds 60 to 75 feet above the conglomerate bed picked by Wilson as the base of the overlying formation, the Marathon lime­stone. The writer concurs with Wilson on the position of the stratigraphic boundary in these localities because the beds above the conglomerates include more limestone and conglomerate and less shale than the beds below. The conglomerates are lentic­ular, however, and cannot he used as defi­nite markers for the base of the Marathon limestone throughout the region. Although the boundary is in a shale-graywacke se­quence in most exposures of the highest beds of the Dagger Flat sandstone and the lowest of the Marathon limestone, the beds below the boundary are typically shale and sandstone with thin beds of limestone and limestone pebble conglomerate, whereas the beds above the boundary are typically limestone, shale, and conglomerate com­posed of slabs and chips of limestone with thin beds of suhgraywacke. The position of the boundary between these two formations as used by both Wilson and the writer is Grapwlite Faunas, Maratlwn Region approximately 50 to 75 feet below that used by King in his maps of the Marathon re­gion. This lower boundary was also used by H. M. Nielsen and members of the Gulf Oil Corporation field party who found it can readily be followed throughout the area. This boundary has been used for a number of years by personnel of summer field parties from several universities. The writer considers that the lower posi­tion of the boundary is justified since it makes the typical shale-graywacke se­quence of the Roberts Ranch member of the Dagger Flat sandstone a more homo­geneous unit and more easily distinguished from the shale, flat limestone chip con· glomerate, and thin-bedded, gray limestone sequence of the lower part of the Marathon limestone. Fossils and Age Most of the fossils found in the Dagger Flat sandstone have come from the Roberts Ranch member. Wilson (1954a, 1956) illustrated and discussed the fauna in de­tail. The only fossil collection from a meas­ured section . of the formation is from 225 feet below the top in a section 4 miles southwest of Marathon. Because he found Geragnostus rudis, G. rudis var. holmi, and an olenid tentatively identified as Lepto­plastus, Wilson correlated these beds with Westergaard's (1947) zones 4 or 5 of the Upper Cambrian of Sweden. However, Wil­son (oral communication), after finding additional and better preserved material in 1957, identified the Tremadoc trilobites Shumardia, Pseu.dohystricurus, Bienbillia, an olenid, and an apatokephaloid pygidi­um from these same beds. King ( 1937, p. 23) stated that Kirk and Resser considered fossils collected from the formation in the Dagger Flat anticlinorium to be Upper Cambriau. Thus, much of the Dagger Flat sandstone is probably Upper Cambrian, but at least the upper part of it is Trema­doc. As Wilson indicated ( 1954a, p. 266, fig. 4), the fauna of the Dagger Flat sand­stone is of great interest because of its Atlantic Province affinities. ORDOVICIAN SYSTEM GENERAL FEATURES The most complete succession of pre­Carboniferous strata of the Marathon up­lift is exposed in the Marathon and Dagger Flat anticlinoria. The higher units in the succession also appear in subsidiary anti­clines south of and between the two anti­clinoria. South and southwest from the main uplifts, in the old Jones ranch, Per· simmon Gap, and Rough Creek areas, Or­dovician rocks are at the surface in the crests of faulted anticlines. Small rem­nants of Ordovician rocks are exposed along the front of the Sierra Santiago which is west and southwest of the Mara­thon uplift. Also, good exposures of Ordo­vician rocks are found in the Solitario, a small dome 50 miles to the south-southwest. The Carboniferous and older strata were intensely folded and faulted so that, although exposures are excellent, complete stratigraphic sections of any formation are difficult to find. During the course of the present field work, twenty-two stratigraphic sections of Ordovician rocks were meas­ured, but only one extends through more than one formation. The exposures on the southeast limb of the Marathon anticli­norium were found to be the least dis­turbed in the entire region. The Ordovician section in the Marathon region is composed of relatively thick beds of shale and thinner beds of dark lime­stone and chert. Intercalated with these beds are lenses of conglomerate, gray­wacke, and exotic boulders. The most abundant fossils are graptolites, but in­articulate brachiopods and a few trilobites are also present. A similar environment existed during Ordovician time in the area of the present Ouachita Mountains (fig. 2), where the Ordovician gection displays a shale, graywacke, and chert lithofacies and a graptolitic biofacies. Different litho­topes existed during Early Ordovician time to the northwest, north, and east of the Marathon region. Two hundred miles to the northwest, the El Paso limestone is nearly all dolomitic limestone character­ized by a fauna of orthoid brachiopods, Bureau of Economic Geology, The University of Texas cephalopods, trilobites, and sponges. The limestone-dolomite sequence of the Ellen­burger has been found in the subsurface 12 miles north of Marathon and is exposed in the Llano region. The Ellenburger has ,a nautiloid, gastropod, and brachiopod biofacies. A thick section of limestones and quartzose sandstones of Ordovician age is exposed in the Arbuckle Mountains in Oklahoma, bearing a brachiopod, trilo­bite, nautiloid biofacies. The Ordovician rocks in the Marathon region consist largely of limestone and shale. The rock succession is, therefore, of a different lithofacies from the surround­ing region, and the fauna is of a different biofacies. Because of this facies difference, correlation of the Ordovician rocks in the Marathon area with Ordovician rocks to the northwest, north, and northeast is diffi­cult. The Ordovician system in the Mara­thon region was divided by King (1931) into five formations; in ascending order r-------1 I Ii I I I I I 0------_JFranklin Mts. T E X ~Beach Mtn. LLANO these are the Marathon limestone, the Alsate shale, the Fort Peiia formation, the Woods Hollow shale, and the Maravillas chert. Graptolites are plentiful throughout the section, occurring in the shales, in all kinds of limestone, impressed on chert and, even rarely, in the quartz sandstones. The ma­jority of the specimens, including the best preserved, were obtained from the lime­stones. With the exception of the Alsate shale, one or more zones have been recognized in each formation, giving a total of fifteen within the Ordovician system. At the outset of any discussion of paleontologic zones, the meaning of the term "zone" should be made clear because "zone" has several meanings-even in hiostratigraphy. A good summary of the history of the use of the word "zone" can be found in Teichert ( 1950). Although Oppel ( 1856-1858) used "zone" to mean a belt of strata de­ Graptolite Faunas, Marathon Regi.on limited by paleontologic criteria, and this usage of the word "zone" has been widely adopted, others (Wedekind, 1916; Fiege, 1951) maintain that a "zone" is a bio­chron, or the life span of a species whose progenitor and descendant are known. Used thus, "zone" is a time term rather than a time-rock term. In the present paper, the word "zone" is used to mean a thickness of rock contain­ing an assemblage of species which does not occur in exactly the same combination in beds aboYe or below. Generally one or more species are restricted to a particular zone. Some species occurring in a given zone range into it from the zone below, while other species range through the zone into the zone above. Still other species range through senral zones. The zone is thus a stratigraphic unit, occurring in more than one locality, characterized by an association of fossils, one of which has been chosen as the name-ghing species or genus. Each zone has not only regional but alw interregional application. Thus the zones presented herein are not merely sub­dfrisions of the local section but are time­stratigraphic units of interregional extent. Figure 3 indicates in a general way the changes in the types of graptolites with the passage of time which give rise to zonal di,-isions. Successively higher zones are marked by the appearance in abundance of a new form or forms. The concept that the entry of new forms may be used to indi­cate the beginning of a new zone is con­sistent with the practice of British and Austrialian graptolite workers. GRAPTOLITE ZONES Fifteen graptolite zones have been de­limited within the Ordo,·ician section in the ~larathon region. These are listed here in ascending order and will be discussed in more detail as they appear in successive formations. The names of the zones and outline figures of the characteristic forms of each are given in figure 3. Zone 1, Anisograptus, is characterized by species of Anisograptus and Clonograptus. The fauna from this zone is sparse in the Marathon re­gion, but in eastern North America it includes Staurograptus, Ra.dio­graptus, and several species of Dictyonema. Zone 2, Adelograptus-Clonograptus. In this zone, the multiramous dicho­graptids reach their zenith. Several species of Clonograptus and Adelo­graptus are found only in this zone, and representatives of the genera Ani.sograptus and Triograptus range into it. Zone 3, T etragraptus approximatus, is marked by the initial phase of tl1e prolific speciation within the genera Didymograptus and Tetragraptus. Several species of T etragraptus are present, of which the most diagnos­tic is r. approximatus. Zone 4, Tetragraptus fruticosus (four­branched form ) , is characterized by the appearance of that distinc­tive species. Many species of Tetra­graptus and Didymograptus are present, and the last representatives of the genera Adelograptus and Clonograptus occur here. Zone 5, Tetragraptus fruticosus (three and four-branched), is marked by appearance of the three-branched form with the four-branched form of this familiar species. The num­ber of species of the Didymograpti and the Tetragrapti reach a maxi­mum in this zone. Zone 6, Didymograptus protobifidus, is marked by the appearance of the first dependent didymograptid, D. protobifidus. Both the four­branched and three-branched forms of T. fruticosus are prominent here. Zone 7, Didymograptus bifidus, is char· acterized by the two dependent didymograptids D. artus and D. bifidus. The numbers of species of both the tetragraptids and didymo­graptids are much fewer in this zone than in the preceding four zones, and the first of the Isograpti appear here. Bureau of Ecorwmic Geology, The University of Texas Zone 8, I sograptus caduceus, is denoted by the development of the large varieties of /. caduceus and by the genera Oncograptus and Cardio­graptus. The first graptolites with a biserial scandent rhabdosome ap­pear here. Zone 9, Hallograptus etheridgei, is marked by the appearance of sev· eral types of biserial scandent rhab­dosome in the genera Glossograptus, Glyptograptus, H allograptus, and Climacograptus. The multiramous dichograptids and the tetragraptids appear for the last time. Zone 10, Glyptograptus cf. G. teretiuscu­lus, is characterized by the wide­spread development of G. cf. G. teretiusculus and Amplexograptus confertus. Phyllograptus makes its last appearance here. Zone 11, N emagraptus gracilis, is marked by the incursion of the genera N emagraptus, Dicellograp· tus, Dicranograptus, and Lepto­graptus, each represented by sev­eral species. The biserial scandent rhabdosome is common in this zone, but species of this type are oveT· shadowed by the other elements. Zone 12, Climacograptus bicomis, is characterized by large diplo­graptids and by C. bicomis with stout spines at the proximal end. The last didymograptids are found in this zone. Zone 13, Orthograptus truncatus var. intermedius, is marked by a "burst" of the large Orthograpti. The pres­ence of Orthograptus calcaratus var. incisus and 0. quadrimucro­natus var. angustus, with or without 0. truncatus var. intermedius, clearly indicates the zone. Zone 14, Ortho.graptus quadrimucro· natus, is characterized by the wide­spread development of that distinc­tive species. The presence of large Orthograpti of the species Ortho­graptus calcaratus with Climaco­ graptus tubuliferus are also indica­ tive of the zone. Zone 15, Dicellograptus complanatus var. omatus, is typified by the as­ semblage of Climacograptus missis· sippiensis,Diplograptus crassitestus, and Orthograptus truncatus var. socialis with the distinctive Dicel­ lograptus complanatus and its va­ rieties. Also, a form like a typical Silurian climacograptid appears in this zone. MARATHON LIMESTONE General Features All the Ordovician rocks of the Mara­thon basin, except the Maravillas chert, were embraced in the "Marathon series" of Baker and Bowman (1917). They· rec· ognized as subdivisions, five members which were numbered but not named, and within this framework Ulrich recognized four faunal zones. In 1931, King aban· cloned the term Marathon series, sub· divided these rocks into four formations, and restricted the name Marathon lime· stone to the lowest of these units. The rela­tion of the two schemes is shown in table I. Only the upper part of the Marathon limestone is exposed at the type locality in the streets and vacant lots of the town of Marathon. Good exposures of the entire formation are easily accessible on the southeast side of the road to Roberts ranch. A complete section of the formation was measured on the east side of a gap between ridges of the Marathon limestone about 2.7 miles down the road toward Roberts ranch from a cairn built where the road turns southwest past the Alsate Creek exposures. The cairn bears S. 25° W. from Iron Mountain and due south from the peak of Cathedral Mountain. The Marathon limestone, as measured in the Marathon anticlinorium, is between 840 and 890 feet thick. There are no com­plete sections in the Dagger Flat anti­clinorium nor in any of the more southerly exposures. The formation is divisible into Graptolite Faunas, Marathon Region STAGE ZONE 15. Dicellogroptus complonotus V. RICHMOND i • MAYSVILLE 14. Orthograptus quodrimucronotus v t EDEN ' 13. Orthogroptus truncotus var intermedius ·TRENTON ' ' v WILDERNESS 12. Climocograptus bicornis .!!Block River in Port -~ v 11. Nemogroptus gracilisPORTERFIELD l \J ' ' 10. Glyptograpfus cf. G. terefiusculusASHBY MAR MOR .i:lchozy ' ' 9. Hallograptus etheridgei I • 8. lsograptus caduceus v v w ' WHITEROCK 7. Didymogroptus bifidus ~ t • 6. Didymograpfus protobifidus A I ~ ., 5. Tetrogroptus fruticosus (3-and 4-branched) ~ A ~ ~ 4. Tetrograptus fruticosus (4-branched) CANADIAN A x SERIES _.._ * H 3. Tetrogroptus opproximotus .-ft-~ 2. Clonogroptus ~ /). -)f x $ I. Anisogroptus ..!./The Wilderness sloge includes the .Block River stage plus !he Rockland limestone of the Trenton stage and equivalents • .!I The Marmor stage includes the Chazy stage and ifs correlatives. Frc. 3. Diagram showing graptolite zones with sketches of the principal species in each. Bureau of Ecorwmic Geology, The University of Texas three parts, the Monument Spring dolomite member and the beds above and below it. The beds below the Monument Spring dolo­mite member range between 530 and 600 feet in thickness and are characterized by thick beds of black shale, many beds of fiat limestone slab conglomerate, beds of medium-to fine-grained, cross-laminated, dark gray limestone, and a few beds of slabby, sublithographic, dark gray lime­stone that weathers a characteristic medium blue gray. lnterbedded with these are some beds 3 to 6 inches thick of sub­gra ywacke composed of subrounded frag­ments of limestone and grains of chert, glauconite, plagioclase, and rounded quartz. The conglomerates (PI. 2, A) are made up of fiat limestone chips and slabs up to 18 inches long and 6 inches wide set in a matrix of coarse-grained, brown, quartz sand. Some of these slabs and chips include graptolites characteristic of the beds immediately below the con­glomerates. The conglomerates and sub­gray°wackes are lenticular and pass later­ ally into beds of shale or limestone. Shale comprises about half of the thickness of this lower member of the Marathon lime­stone in the Marathon basin; in outcrops south of the basin, the amount of shale in­creases progressively and includes beds of subgraywacke. In the old Jones ranch ex­posures, shale with some limestone beds makes up nearly two-thirds of the thick­ness, and in the Solitario, subgraywackes and shales are even more prominent in the lower part of the Marathon limestone. The Monument Spring dolomite mem­ber was named by King (1931, p. 1068) for its exposure half a mile west of Monu­ment Spring, 12 miles west of Marathon. It occurs about 550 to 600 feet above the base of the Marathon limestone and ranges from 40 to a maximum of 90 feet in thick­ness. It consists of oval lenses of blue-gray and yellow-mottled dolomitic limestone surrounded by black shale and thin-bed­ded, cross-laminated, gray limestone. The lenses of dolomitic limestone are present throughout much of the Marathon anti­clinorium, but they gradually disappear southeastward in the Dagger Flat anticli­norium. Black shale and thin-bedded, gray limestone are equivalent to the member in the Solitario and old Jones ranch areas. The upper member of the Marathon limestone, about 250 feet thick, consists of characteristic blue-gray weathering, dark gray, sublithographic limestone in beds 4 to 8 inches thick interbedded with thin­bedded, cross-laminated, dark gray lime­stone in layers 4 to 6 inches thick and a few beds of black shale and fiat limestone slab conglomerate. To the south, in the old Jones ranch and Solitario exposures, the upper part of the Marathon limestone in­cludes many beds of arenaceous limestone and more shale than in the Marathon basin. Local, Features Marathon anticlinorium.-The Mara· thon limestone is best displayed in the roll­ ing hills southeast of the road to Roberts ranch. It is closely folded and much faulted; one of the most spectacular ex­ amples of the folding and faulting is dis­ played at the well-known outcrops on Al­ sate Creek. The beds below the Monument Spring dolomite member contain more shale and limestone slab conglomerate lenses and less limestone, particularly less sublithographic limestone, than the beds above it. The basal 300 feet of the formation is primarily interbedded black shale, buff, calcareous shale, and limestone slab conglomerate lenses with a few beds of thin-bedded, cross-laminated, gray limestone and a few lenses of coarse-grained, brown subgray· wacke, 4 to 24 inches thick. Higher in the section, limestone beds become increas­ ingly numerous. Also, beds of blue-gray­ weathering, dark gray, sublithographic limestone appear and increase in number upward toward the Monument Spring dolo­ mite member. Occasional lenses of pebbly, light gray, oolitic limestone are found low in the section. They have a fauna of trilo­ bites and molluscs in contrast to the grapto­ lite fauna in the surrounding rocks. Graptolite Fa~mas, Marathon Region Plate 2 A Limestone chip conglomerate lens in the Marathon limestone. (Photograph by D. B. Clarke) B Alsate shale at its type locality on Alsate Creek. The hammer is lying on a conglomerate lens at the top of the Marathon limestone. Graptolite Faunas, Marnthon Hcgion Plate 3 A Anticlinal valley in the Woods Hollow shale on the cre;;t of Simpson Springs Mountain. B Typical exposure of the Maravillas chert. Black chert is interbeddcd with gray-weathering limestone. (Photograph hy D. B. Clarke) Table 1. Relation of nomenclature applied to Cambrian and Ordovician rocks in the Marathonregion. After King (1931, p. 1066). Ulrich (in Baker end Sy1tem King (1931) Baker and Bowman (1917) Bowman, 1917) Mara villas chert Maravillas chert Zones 5 and 6 Zone 4 Woods Member 4 Member 5 Hollow shale Zones 1 and 2 in Brewster formation Member 1 and boulders Fort PenaNot seen formation Mara- Ordovician th on AlsateNot seen series shale Marathon part of the Marathon Zone 3 Member 3 is a small limestone limestone (a) upper member (b) Monument Spring dolomite (c) lower member Cambrian Member 2 Dagger Flat sandstone ~ .., .§ s - ~· .f ~ .., ~ ., :=ti ~ s· ., i­ w Bureau of Economic Geology, The University of Texas The conglomerate lenses are similar in appearance above and below the Monu­ment Spring dolomite member. Locally, the lenses reach 10 to 15 inches in thickness; they extend from a few feet to several yards along strike. The slabs within the con­glomerate consist of thin-bedded, cross­laminated, dark gray limestone and blue­gray-weathering, sublithographic lime­stone, are elongate with maximum dimen­sions of 18 inches in length and 6 inches in width, and lie subparallel to one another in a matrix of coarse brown sandstone con­taining rounded chert pebbles. The sub­graywacke lenses also are similar above and below the Monument Spring dolomite member. They are composed of small frag­ments of shale, limestone, other arenites, rounded quartz grains, plagioclase, biotite, glauconite, chert, and sericite with calcite and phosphate cement. No graded bedding was seen. Thin, buff, argillaceous limestone layers found sporadically throughout the section have well-developed mud cracks. The weathered surfaces of some of the lime­stone beds are thickly strewn with sepa­rated hexactinellid sponge spicules, where­as other limestone bedding surfaces show minute channel markings and are overlain by one-eighth to one-quarter-inch layers of sandstone. Commonly such sandstone layers are crowded with worn, broken shells of inarticulate brachiopods. The Monument Spring dolomite mem­ber is 94 feet thick near Alsate Creek and ranges from 40 to 60 feet in thickness in the northern part of the Marathon anti­clinorium but thins southward, being only 25 feet thick at Monument Spring, the type locality. The member consists of oval lenses of dense, gray, dolomitic limestone aligned subparallel to each other separated by shale and thin-bedded, cross-laminated, gray limestone. The weathered surface of the dolomitic limestone has a blue-gray and yellow-mottled appearance, and where re­placement by silica has occurred it weath­ers to a characteristic orange-brown color. The individual lenses range in size from 10 feet long and 5 feet wide to 50 feet long and 25 feet wide. In some places the lenses are separated from one another by several feet of shale or thin-bedded limestone, but in other places, several lenses lie close to­gether and overlap each other. Fossil frag­ments are common in places in the dolo­mitic limestone-there are vague algal structures, sponges of the type of Arche­oscyphia, orthoid brachiopods, and cepha­lopods. The oval masses that characterize the Monument Spring member were prob­ably patch reefs constructed principally of algae and sponges. Although small blocks of the dolomitic limestone occur. higher in the section, it is predominantly at one horizon, and that horizon lies entirely within one graptolite zone. In the beds above the Monument Spring dolomite member, blue-gray-weathering sublithographic limestone in layers 4 to 8 inches thick predominates. Of nearly equal importance are layers of medium-to fine­grained, thin-bedded, cross-laminated, dark gray limestone, 3 to 6 inches thick, exhibit­ing a few slump structures. The slump structures do not extend laterally for more than 10 feet in any one bed. Beds of black shale, buff argillaceous limestone, and buff to orange-weathering black limestone and lenses of flat limestone slab conglomerate and subgraywacke are subordinate rock units in the upper part of the formation. Two layers of black chert, each about 1 inch thick, occur near the top of the forma­tion in the northern part of the southeast limb of the Marathon anticlinorium. A few blocks of characteristic Monument Spring dolomitic limestone are found in this upper member and are commonly associated with a conglomerate or sandstone lens. Most of the blocks are 6 to 18 inches long and in some places they extend discontinu­ously for as much as 20 feet along the strike. Dagger Flat anticlinorium.-The Mara­thon limestone is so intensely folded and faulted in its exposures in the Dagger Flat anticlinorium that no continuous section can be measured on the northwest limb and only a partial section of the lower part of the formation can be measured on the southeast limb. The rocks comprising the Grapwlite Faunas, Marathon Region Marathon limestone here exhibit the same lithologic relations and details as they do in the Marathon anticlinorium except that the Monument Spring member includes more shale and thin-bedded, gray lime­stone and less gray, dolomitic limestone. No determination of thickness for the for­mation is possible in this anticlinorium. On the northwest limb, younger beds of the Marathon limestone appear in the troughs of synclines and older beds appear in the crests of adjoining anticlines. The section is repeated many times with pro­gressively older beds appearing in the sub­sidiary anticlines and synclines going from the limb toward the center of the anticli­norium. The Threemile Hill thrust fault can be traced eastward several miles from the base of Threemile Hill along the southeast limb of the Dagger Flat anticlinorium. A collection of graptolites characteristic of the upper part of the Marathon limestone was obtained from a shale outcrop at the base of Threemile Hill. At a locality 3 miles northeast of Threemile Hill and 2 miles northeast of Buttrill ranch, graptolite collections were made from a measured section. Zonal determination of the grapto­lites indicates that the uppermost 30 feet of the Marathon limestone rests on the basal 340 feet. Therefore, most of the upper part of the formation, the Monument Spring member, and almost half of the lower part of the formation are missing. Thus King's observation (1937, p. 29) that the Mara­thon limestone thins to 350 feet on the southeast limb of the Dagger Flat anticli­norium has a structural and not a strati­graphic explanation. Ten miles southwest of Peiia Blanca Spring, six collections of graptolites were made in a traverse of 1,200 feet across the strike of the beds. Each collection belonged to the same grap­ tolite zone, thus demonstrating tight iso­clinal folding. Old /ones ranch and Solitario areas.­ Completely folded and faulted Ordovician rocks crop out under the Cretaceous rim in an arroyo which is about 2 miles S. 20° E. from the present Slaughter ranch head­quarters (formerly old Jones ranch). These are the most complete and extensive out· crops of the older Paleozoic rocks southeast ofthe Marathon uplift. Wilson ( 1954b) de­ scribed the exposures in this area and in the Solitario. However, collections of grap­ tolites made by the writer have made pos­ sible a more detailed understanding of the Ordovician stratigraphy in these regions. In both areas the lower part of the Mara­thon limestone includes calcareous sub­graywacke interbedded with the typical shale, flat limestone slab conglomerate, and limestone sequence. The dolomitic lime­stone of the Monument Spring member is not present in either area, and the member is equivalent to interbedded black shale and thin-bedded, cross-laminated, gray limestone. In these southern exposures the upper part of the formation has more shale and more thin-bedded, cross-laminated, gray limestone in relation to blue-gray­weathering, dark gray, sublithographic limestone than in the main uplift. Thick beds of subgraywacke and brown-weather­ing arenaceous limestone occur in the upper part of the formation in both areas; and in the Solitario, several beds of chert are included in the upper part of the for­mation. In summary, the Marathon lime­stone is more elastic in the Solitario and old Jones ranch areas, with shale and sub­graywacke the predominant rock types at the top and the base of the formation. Fossils and Age The fauna of the Marathon limestone in­cludes two distinct facies. The Monument Spring dolomite has a fauna of sponges, brachiopods, and nautiloids, and the rest of the formation bears graptolites, inarticulate brachiopods, and trilobites. Except in the Monument Spring member, graptolites dominate. The best-preserved specimens occur in limestones, most commonly those of sublithographic texture. In all, seven graptolite zones have been delineated in the Marathon limestone, two below the Monu­ment Spring dolomite and four above it. The complete fauna is given in the follow­ing check list (p. 16). The lowest zone, that of Anisograptus, Zonal distribution of species in the Marathon limestone SPECIES ZONE' 1 2 3 4 5 6 7 Adelograptus hunnebergensis (Moberg) ? -----·---------­x Adelograptus pusillus (Ruedemann) -----------------------­x Adelograptus simplex (Tornquist) ---------------·-------------­x Adelograptus victoriae (T. S. Hall) -----------------·---------­x Anisograptus dissolutus Berry, n.sp. -· ---------------------­x Bryograptus crassus (Harris and Thomas)? -----------­x Clonograptus flexilis (Hall) ····-·----·---·-·------·-·-·-------···-· x x x Clonograptus persistens Harris and Thomas -------------­x Clonograptus rigidus (Hall) ----------·-·--··--·-----··------------­x x Clonograptus cf. C. tenellus (Linnarson) ---·---·-------­x Clonograptus tenellus var. callavei (Lapworth) -------­x Dichograptus octobrachiatus (Hall) -------·-----------------­x x x x Dictyonema dumosus Berry, n.sp. -·---·-----·-·-----------------· x Didymograptus artus Elles and Wood -----------------------­x Didymograptus bifidus (Hall) ----------------------·------------­x Didymograptus denticulatus Berry, n.sp. ------·----------­x Didymograptus ellesae Ruedemann -----·-···-··--·--·--------­x Didymograptus extensus (Hall) -··---·---------·--------------­x x x x Didymograptus leptograptoides Monsen ---------·---------­x Didymograptus nicholsoni Lapworth -·-··-·---·-·--·--·----­x x x Didymograptus nicholsoni var. planus Elles and Wood ·····-·-·-·-·--······--·-·--·---·--·------·-····-·-·---------·--x x Didymograptus nitidus (Hall) -·-----···--·---·-···--·---·-·-·--·­x x x x Didymograptus novus Berry, n.sp. ---·--···--------------------· x Didymograptus patulus (Hall) --·---------··-----·-------·-------­x x x Didymograptus protobifidus Elles ---------------·--·----------­x Didymograptus protoindentus Monsen -------·-------------­x Didymograptus similis (Hall) -------·-·---··--···-------------·-­x x x Goniograptus perflexilis Ruedemann --------··---------------­x Gonigraptus thureaui (McCoy) -----·-------------------····-··-­x Isograptus caduceus var. lunata Harris -------·-----·-------­x Phyllograptus angustifolius Hall -------·-----·--·-------··--·--­x x Phyllograptus anna Hall ·-·--··-·---·---·······--·--·---·---·-------·­x x x Phyllograptus anna mut. longus Ruedemann ---··--·---­x Phyllograptus ilicifolius Hall ------·-----------·----···-----------­x x x x Phyllograptus typus Hall -·-·--------------·--·-----·-----------------­x x Ptilograptus plumosus Hall ---···--·---·---·-------------·------·---­x Tetragraptus acclinans Keble ---··------------·-···-·---·-·-------­x Tetragraptus amii Lapworth ·-·--·-------·-·-----··----·-----------­x x x Tetragraptus approximatus (Nicholson) -------------··--­x Tetragraptus bigsbyi (Hall) -··---··--·--·-------·---·---·--------·­x x x x x Tetragraptus decipiens T. S. Hall --····----·--------·-----·-·-­x Tetragraptus decipiens var. bipatens Keble and Harris ·--·-·----··--····---··-···----···-----·····--·-··---·---·------x Tetragraptus fruticosus ( 4-branched form) (Hall) x x x Tetragraptus fruticosus (3-branched form) (Hall) x x Tetragraptus pendens Elles -···-·----····----··-·-··--·----------·---·­x Tetragraptus pygmaeus Ruedemann ---·-----·-------·------·· x x Tetragraptus quadribrachiatus (Hall) --··---·-------------­x x x x x Tetragraptus reclinatus Elles and Wood --··---·-····------­x Tetragraptus serra (Brongniart) ·-··------·-·-····-·-·---·-·-·-­x x x Tetragraptus taraxacum Ruedemann --··-------······-··---­x x x Triograptus cf. T. otagonensis Benson and Keble .... x x Trochograptus lapworthi Ruedemann ------·---·-·--·-·-·---­x Parabolinopsis mariana Hoek -·----··-··-·-···--·---------·------·­x Beltella latifrons Wilson ··-··--·-···--·--·----·-·--·---·---·----·--·--x Bellefontia sp. --···---·-----·--------------·-----------·-··-·-----·-------·-··-­x Kayseraspis sp. -·----·---····-·-----··---··------··--------------·---··--------x Lloydia sp. -··-----··---·-----··---··--···--·-----·-·-------·--------·-----·--·---· x Protopliomerops sp. ----·-·-··---··--·-··---··-··---------·----··-·----·-·-­x New genus related to Benthamaspis --··-·-------------------­x Symphysurina cf. S. woosteri Ulrich -·-·------·---·----·--··--x Ophileta sp. -··-·--·-·----·-········---------·-----------·--·-·------·---·---·---­x Tostonia sp. ·-··-·---·-·-··---···--·----·--·-·-·-·-···-----------------··-·----·-­x Endoceras sp. ·--·-----··----·----·--··-----·-··---··----·--·-------·------·----x Pachendoceras sp. -··---··--·--···-··-·-····-·--··-----·--------·---··--·--­x Shumardoceras sp. ·-···--····-···--·--··-··-·-·····---··--·--·---·-·-·-·----x Archeoscyphia aff. A. annulatum Cullison ------·-------·­x Finkelnburgia sp. ·---·---······--·-··-·-·--·----·-------·---·----------------x 1 Esplanalion of the various zone1 in thit and similar li1ll ii 1i·nn ia &gure 3 and on pp. 7-9. Graptolite Faunas, Marathon Region has a rather sparse assemblage of species, seemingly because the basal beds of the formation are more elastic. Anisograptus is the typical genus here but is usually ac­companied by Clonograptus cf. C. tenellus and Trwgraptus. Several pygidia and ceph­alons of Belle/ ontia sp. and Lloydia sp. were collected from the upper part of this zone. The zone is well developed at localities 6, 29, 118, and 119 (see Appendix). Near the contact between this zone and the next above, the faunas intermingle so that a pre­cise boundary is difficult to locate, but the zone is approximately 200 feet thick. Wil­son (1954a) recorded Parabolinopsis mariana from 163 feet above its base in measured section I (Appendix). The second zone of the Marathon lime· stone is characterized by several species each of the genera Clonograptus and Adelograptus. Early representatives of the genera Tetragraptus and Didymograptus are found here also. Typical zonal assem-. blages were obtained in collections 2, 11, 12, 33, 37, 74, and 84. Wilson (1956, p. 1348) recorded Kayseraspis, Symphy­ surina cf. S. woosteri, Beltella latifrons, Tostonia, Ophileta, and Finkelnburgia from the locality of collection 34. The writer collected Ophileta and a Pachen­ doceras from the same locality. Zone 2 ranges from 330 to 400 feet thick. Zone 3 and the succeeding four zones are characterized by a burst in speciation within the genera Didymograptus and Tetragraptus. Three species of these gen· era range through all five zones, but the majority of the species are confined to only two or three zones. The appearance of certain combinations of species of Tetra­graptus and DUlymograptus with species of other genera are diagnostic enough so that five zones have been recognized in the upper 290 to 340 feet of the Marathon limestone. The third zone is characterized by the appearance of several species of Didymo­graptus and T etragraptus and by the per­sistence of two species of Clonograptus from the zone below. The most diagnostic species is T etragraptus approximatus, and the base of the zone is picked by its first appearance. Good collections of the typi­cal species of the zone were obtained from localities 76, 77, 120, and 130. In the Marathon anticlinorium, the typi­cal zonal assemblages collected from shale_s and limestones interbedded with the Monu· ment Spring dolomite indicate that the member lies completely within zone 3. Good collections of the typical zone as­semblage have been made in the old Jones ranch and Solitario areas, where the Monu­ment Spring member is not present. For the most part, the fauna of the Mon­ument Spring dolomite member is of a dif­ferent biofacies from that of the other two members of the Marathon limestone. It contains sponges, orthoid brachiopods, cephalopods, gastropods, and some algal masses. Kirk (1934, p. 451) indicated that the characteristic sponge-cephalopod fauna of the lower part of the El Paso limestone is well developed in the Monument Spring member of the Marathon limestone. He stated that: "Calathium, Piloceras, and Colpoceras are 1epresented by identical species with those in the lower El Paso." King (1937, p. 30) reported masses of Cryptozoon, Calathium cf. C. formosum and two other species of sponges, and unde­termined species of orthoid brachiopods and gastropods from the Monument Spring member. Cloud and Barnes {1948, p. 64­66) obtained Calathium, cystoid plates and columnals, Diaphelasma sp., "Orthis" sp., Allopiloceras cf. A. coarctum, fragments of other piloceratid cephalopods, and a tro­cholitid cephalopod from the member. The writer has collected Shumardoceras, Endo­ceras, and Archeoscyphiaaff.A. annulatum Cullison from the Monument Spring mem­ber as well as unidentified fragments of orthoid brachiopods, cephalopods, and sponges. The fauna is preserved as silic­ified fragments on the surface of the dolo­mitic limestone and is thus hard to collect. Sponge remains are relatively abundant and can be found in many of the exposures but other fossils are rare. Zone 4 is characterized by the appear­ Burea:u of Ecorwmic Geology, The University of Texas ance of additional sp~cies of the genera T etragraptus and Didymograptus and by the last appearance of Clonograptus and Adelograptus. The most widespread and typical species of this zone is the four­branched form of Tetragraptus fruticosus. The typical zonal assemblage was found best developed in collections 69 and 71. The lower boundary of the zone is defined by the first appearance of the four­branched form of T etragraptus f ruticosus while the upper boundary is placed at the first appearance of the three-branched form of this species. Zone 4 is about 30 feet thick. The fifth zone is characterized by the ap­pearance together of the three-and four­branched forms of Tetragraptus fruticosus. Also, the Phyllograpti are represented by three species, two of which appear for the first time. Two specimens were found of a trilobite which is similar to a species of the genus Protoplwmerops figured by Ross (1951, pl. 31). Good collections were ob­tained in the Alsate Creek section (meas­ured section XVIII, collections 26 and 27) and at localities 66, 90, and 91. The zone is about 40 feet thick. Zone 6 is marked by the appearance of the dependent didymograptid Didymo­graptus protobifidus with the three­branched form of Tetragraptus fruticosus. Several species of the Tetragrapti and of the Didymograpti are seen for the last time in this zone for the burst of speciation in these two genera is over. The dependent type of Didymograptus makes its first ap­pearance here. Typical zonal assemblages were found in the Alsate Creek section (measured section XVIII, collections 22, 23, 24F, and 25), and in fossil collections 40, 52, 63, and 64. The zone, the thickest of those above the Monument Spring mem­ber, is about 140 feet thick. The seventh zone is delimited by the well-known and widespread species Didy­mograptus bifidus and Didymograptus artus. Other species of dependent Didymo­grapti are present, while the extensiform Didymograpti are now represented by fewer species than before. Phyllograptus typus is common, and the first of the lso­grapti appear here. The minute form /. caduceus var. lunata is infrequently found with the typical zonal assemblage. Good collections from this zone were secured at Alsate Creek (measured section XVIII, collections 19, 20, and 24A) and at lo­calities 47, 67, and 70. The zone is 30 feet thick. The Alsate Creek exposures afforded the best collecting in the entire area. The sec­tion yielded graptolites in nearly every inch of rock from the Monument Spring member to the Alsate shale, permitting very detailed zonal determinations for the beds above the Monument Spring member. Turner (1940) described a trilobite (Se· leneceme bakeri (Turner) ) , from the Marathon limestone below the Alsate shale at the Alsate Creek section; it probably came from either zone 6 or zone 7. Kindle (1942) described a similar trilobite (Se­leneceme evansi (Kindle) ) from Canada where it was collected from beds contain· ing Didymograptus bifidus, suggesting an affinity with zone 7 of the Marathon se­quence. Shelly fossils are not common enough in the Marathon limestone to permit detailed correlation between the graptolite zones and sequences where the shelly fossils are dominant. The lower part of the Marathon limestone, however, has yielded a few diag­nostic trilobites. Wilson (1954a) collected the Tremadoc species Parabolinopsis mari­ana from beds that are in graptolite zone 1, and the writer collected Bellefontia and Lloydia from the same zone. The Belle­f ontia indicates a possible correlation with the Gasconade dolomite of the standard Lower Ordovician section for North Amer­ica. The assemblage of Pachendoceras, Symphysurina cf. S. woosteri, Ophileta, and Finkelnburgia from the lower part of graptolite zone 2 also correlates with the Gasconade dolomite. Graptolite zone 1 and at least part of zone 2 are equivalent to the Gasconade dolomite. Further, the presence of Bellefontia and Symphysurina cf. S. woosteri indicates a correlation of zone 1 and a part of zone 2 with Ross' zones A and Graptolite Faunas, Marathon Regi,on B of the Garden City limestone in north­eastern Utah. The fauna of the Monument Spring member, although of a shelly biofacies, is poorly preserved so that accurate correla­tion of it is difficult. Kirk ( 1934, p. 451) correlated it with the lower part of the El Paso limestone of the Franklin Mountains. Cloud and Barnes (1948) were only able to assign post-Tanyard age to the assem­blage which they collected from the mem­ber. The evidence from the cephalopods indicates a Middle or Late Canadian age. The genus Piloceras is restricted to the Ca­nadian as is the genus Allopiloceras. All known species of the genus Shumardoceras have come from the upper part of the Jef­ferson City group or equivalent beds. The presence of sponges similar to Archeo­scyphia annulatum indicates a possible cor­relation with the Rich Fountain formation. Further, the writer compared sponges from the Monument Spring member with sponges from the middle part of the Kind­blade limestone in the Arbuckle Mountains and is of the opinion that similar forms are present in both areas. The Kindblade limestone has been correlated with the Jef­ferson City group. In summary, zone 3, which includes the Monument Spring member, is considered a correlative of the Jefferson City group. There are no shelly fossils of value in correlation in the Marathon limestone above the Monument Spring member. However, Didymograptus protobifidus, which is characteristic of zone 6, has been recognized by Decker in the Smithville limestone of the standard Lower Ordo­vician section and in the West Spring Creek formation in the Arbuckle Moun­tains. Didymograptus artus and D. bifidus, the diagnostic elements of zone 7, are re­corded from the Joins formation in the same area (Ruedemann, 1947, p. 88). Cooper (1956, p. 119) assigned the Joins formation to the early Middle Ordovician, Whiterock stage. Didymograptus bifidus, the characteristic species of zone 7, is listed by Ross (1951, p. 27) in zone M, which is present in the Swan Peak formation in northeastern Utah. Cooper (1956, p. 130), because of the presence of Anomalorthis in the fauna, placed the Swan Peak formation in the Whiterock stage. Ruedemann (1947, p. 327) reported D. bifidus from the Black Rock limestone of the standard section for the Lower Ordovician. Graptolite zones 4 and 5 lie between two zones which have been correlated with units in the standard section for the Lower Ordovician; thus these zones are possible correlatives of the Cotter and Powell formations in the Ozark region. Tremadoc fossils have been found 25 feet above the contact of the Marathon limestone with the Dagger Flat sandstone and 225 feet below the contact. If the Tremadoc belongs in the Ordovician, as is now commonly considered, then, with the exception of the uppermost graptolite zone, the Marathon limestone is Early Ordo­vician. The top 30 feet is Whiterock (early Middle Ordovician) age. ALSATE SHALE General Features King (1931, p. 1069) named the Alsate shale for Alsate Creek (Pl. 2, B) ex­posed in the bank of the creek, 211z miles west of the Picnic Grounds, 5 miles south­southwest of Marathon (Pl. 1). It is a black shale that forms a distinct break between the characteristic blue-gray-wea­thering Marathon limestone and the tan­weathering limestones and calcareous sandstones of the Fort Pena formation; in most places, it occupies a covered inter· val between outcrops of these formations. Local, Features Marathon anticlinorium.-ln the Alsate Creek exposure, a conglomerate underlies the black shale and was included in the Alsate shale by King. However, the con­glomerate is merely a lens which can be traced into the blue-gray-weathering, dark gray, sublithographic limestone at the top of the Marathon limestone and it thus be­longs there and not in the Alsate shale. In this anticlinorium, the Alsate shale is well indurated, greenish weathering, and Bureau of Ecorwmic Geology, The University of Texas breaks into small rhomboid chips. It is about 100 feet thick in Alsate Creek and in exposures on the ridge east of the road to Roberts ranch but thins to 85 feet 3 miles to the southwest. Dagger Flat anticlinorium.-The Alsate shale is much thinner and commonly oc­cupies a covered interval in this area. It is a greenish-weathering black shale. The granular limestone layers containing Onco­graptus, which King (1937, p. 31) de­scribed as a part of the formation, belong to the overlying Fort Pefia formation. Fossils and Age The formation contains a sparse grapto­lite fauna. The best collections came from the outcrop in Alsate Creek (measured section XVIII, collection 18) where Iso­graptus caduceus var. lunata, Phyllograp­tus typus, T etragraptus amii, Didymograp­tus a/finis, and Didymograptus mendicus were collected. Isograptus caduceus var. lunata was also collected from several other exposures of the formation and is the most common fossil in it. This fauna is transitional between that of the Didymograptus bifidus zone and that of the I sograptus caduceus zone, be­cause it has species which are character­istic of both. However, the writer considers it to be more closely related to that of the I. caduceus zone and it therefore is includ­ed in that zone. The formation falls within the Whiterock stage of Cooper as does the rest of the /. caduceus zone. RODRIQUEZ TANK SANDSTONE In the Solitario and old Jones ranch areas the black Alsate shale is not present between the characteristic limestones of the Marathon limestone and the Fort Pefia formation; in its place is a white to buff quartzose sandstone that ranges from 20 to 50 feet in thickness. The sandstone is composed of well-rounded quartz grains. Graptolites characteristic of the uppermost part of the Marathon limestone were col­lected 3 inches below the sandstone, and graptolites diagnostic of the basal beds of the Fort Pefia formation were collected 1 inch above the sandstone in both areas. Thus the exact stratigraphic position of the sandstone has been determined from paleontologic evidence. Although the sandstone is well exposed outlining a recumbent anticline under the Cretaceous rim in the old Jones ranch area, that exposure is not easily accessible. Therefore, the writer designates the north­ern part of the Solitario as the type locality and names the formation the Rodriquez Tank sandstone for its outcrops near the Rodriquez Tank shown on the map of the Solitario by Wilson (1954b, p. 2464). A measured section that shows the strati­graphic relation of the sandstone to the underlying and overlying formations is not given because of the structural complexity of the northern part of the Solitario. Sand­stone lenses which locally appear similar to the Rodriquez Tank sandstone are pres­ent in the upper part of the Marathon lime­stone in both the Solitario and old Jones ranch areas. However, the Rodriquez Tank sandstone is a continuous unit and com­monly stands out forming a low ridge in the area of Ordovician outcrop in the Soli­tario and a prominent bench in the old Jones ranch locality. FORT PENA FORMATION General Features The Fort Pefia formation forms low prominent ridges throughout the Marathon basin. King (1931, p. 1070) designated one of the ridges directly north of old Fort Pefia Colorada as the type locality. The for­mation has been so intensely deformed­commonly occurring in the crests of anti­clines or troughs of synclines-that there are few places where more than a few feet crop out. The most complete exposures are along the southeast limb of the Marathon anticlinorium, but even here, the upper contact is seldom seen. A 229-foot section of the formation was measured on the southeast limb of the Marathon anticli­norium 2% miles west of the Picnic Grounds (Pl. 1), and 225 feet were meas­ured 3 miles to the southwest. The formation consists of alternating Graptolite Faunas, Marathon Regi-On purple chert in layers 2 to 6 inches thick, black shale in layers 4 to 24 inches thick, brown-weathering, thin-bedded, generally cross-laminated, gray limestone in layers 4 to 18 inches thick containing orange­weathering chert stringers one-quarter to three-quarters inch thick, calcareous sub­graywacke in layers 4 to 17 inches thick, and limestone and chert-pebble conglom­erate in layers 3 to 10 inches thick. There is no rhythm to the alternations of lith­ologies; one rock type extends for several yards along strike and then passes into an­other rock type. The lithologic character of the Fort Peiia formation is remarkably uniform over its outcrop in the Marathon uplift. In the Solitario and old Jone.-. ranch areas it includes thicker and more numerous shale and sandstone beds. Local Features Marathon antU:linorium.-In this anti­clinorium, the formation forms secondary ridges below those of the white Caballos novaculite. A ridge of the Fort Peiia for­mation parallels a ridge of the novaculite along the southeast flank of the Marathon anticlinorium. North of the town of Mara­thon, the formation crops out in hills of synclinal structure. The base of the forma­tion in the northern part of the anticli­norium is marked by a layer of conglom­erate 6 to 10 feet thick composed of chert and limestone pebbles one-quarter inch to 6 inches in diameter set in a gray arenace­ous limestone matrix. Black shale or brown­weathering, gray, thin-bedded limestone is the basal bed of the formation in most places in the southern part of the anticli­norium. The shale beds increase in number and thickness near the top of the forma­tion. Dagger Flat antU:linorium.-Here the formation has been intensely folded so that typical exposures are found in low ridges that structurally are either troughs of syn­clines in subsidiary folds involving the Alsate shale and the upper part of the Marathon limestone or crests of anticlines in subsidiary folds involving the Woods Hollow shale. A conglomerate bed is pres­ent at the base of the formation in a few places, but in most, the basal unit is a brown-weathering, thin-bedded, gray lime­stone with orange-weathering chert string­ers. Old I ones ranch and Solitario areas.­ The Fort Peiia formation in the old Jones ranch and Solitario areas consists of the alternating brown-weathering, thin-bed­ded, gray limestone, purple chert, limestone pebble conglomerate, and black shale beds that are so characteristic of the formation in the Marathon basin. However, the shale beds are much thicker (up to 60 feet in thickness) and more numerous. A few thin beds of blue-gray-weathering, dark gray, sublithographic limestone are included near the base of the formation. Fossils and Age The limestones and shales of the Fort Pena formation contain graptolites and a few gastropods, ostracods, brachiopods, and conodonts. In some of the limestones, uncompressed or partially compressed biserial graptolite rhabdosomes have been preserved. These rhabdosomes have been highly carbonized so that no morphological details can be observed, and fine-grained white quartz sand now fills them. The lime­stones in which such rhabdosomes are found contain only a few scattered grains of quartz sand. The rhabdosomes appar­ently were filled with quartz sand and then transported into the area of limestone dep­osition. The uncompressed state of such highly carbonized remains is doubtless the result of the sand filling. Enough distinctive assemblages of grap­tolites were collected from different levels in the formation so that two zones and part of a third may be proposed. The following check list (p. 22) includes all the graptolite species found in the formation and their zonal occurrence. The basal beds of the Fort Pena forma­tion are characterized by I sograptus cadu­ceus var. victoriae, the typical form of /. caduceus and the name-giving species of the zone, and by the larger and more robust Bureau of Economic Geology, The University of Texas varieties /. caduceus var. maxima and /. caduceus var. maximo-divergens. The gen· era Oncograptus and Cardiograptus are also characteristic of this lowest zone of the formation. Good collections of the typi­cal zone fossils were made at localities 95, 107, llO, 140, and 141. The second zone of the Fort Pena for­mation is characterized by the appearance of graptolites with a slender biserial scan­dent rhabdosome. Hallograptus etheridgei, the name-giving species, Glyptograptus in· tersitus, and Trigonograptus ensiformis are characteristic forms. Other common species are Glossograptus acanthus, Glypw­graptus cf. G. austrodentatus, Cryptograp· tus schaf eri, and Didymograptus nodosus. The Tetragrapti continue to be represented by T. quadribrachiatus and T. serra, but this is the last appearance of the tetragrap· tids in the section. The multiramous dicho· graptids also are seen for the last time in Zonal distribution of species in the Fort Pena formation SPECIES 8 Amplexograptus confertus (Lapworth) -----------------------------------------­Amplexograptus cf. A. differtus Harris and Thomas -------------------­Brachiograptus etaformis Harris and Keble ----------------------------------Cardiograptus crawfordi Harris_____ --------------------------------------------------x Cardiograptus morsus Harris and Keble ----------------------------------------x Climacograptus riddellensis Harris _______ ------·----------------·----------------Cryptograptus schaferi (Lapworth) -----------------·-----------------------------­Dichograptus marathonensis Berry, n.sp. -------------------------·----------­Dichograptus octobrachiatus (Hall) ----------------------------------------------­Didymograptus compressus Harris and Thomas ---------------------------­Didymograptus cuspidatus Ruedemann ------------------------------·----------­x Didymograptus euodus Lapworth ----------------------------------------------------x Didymograptus nodosus Harris ---------· ___ -----------------------------··----------Didymograptus pacificus Ruedemann ----------------------------------------­x Didymograptus paraindentus Berry, n.sp. ------------------------------------x Didymograptus v-deAexus Harris _______ _____ ----------·-------------x Glossograptus acanthus Elles and Wood ____ ------------------------------Glossograptus hincksii (Hopkinson) -----------··-------------------------------­Glossograptus horridus Ruedemann ------------------------------------------­Glossograptus hystrix Ruedemann ------------------------------------------------­Glyptograptus cf. G. austrodentatus (Harris and Keble) x Glyptograptus intersitus Harris and Thomas _-----------------------------­Glyptograptus cf. G. teretiusculus (Risinger) ------------------------­Isograptus caduceus var. divergens Harris -------------------------­x Isograptus caduceus var. imitata Harris -----------------------------------------­Isograptus caduceus var. maxima Harris _----------------------------­x Isograptus caduceus var. maximo-di,-ergens Harris ---------------------­x Isograptus caduceus var. victoriae Harris ----------------------------­x Isograptus forcipiformis var. latus Ruedemann ------------·--------------­Isograptus manubriatus (T. S. Hall) --------------------------------------------­x Isograptus ovatus (T. S. Hall) _ ----------------------------------------Hallograptus echinatus (Ruedemann) ____________________ ·-------------------Hallograptus etheridgei (Harris) -------------------------------------------Loganograptus logani (Hall) --------------_________ -------------------------· Loganograptus logani mut pertenuis Ruedemann ------------------------Oncograptus upsilon T. S. Hall _________ ------------------------------------------x Oncograptus upsilon var. biangulatus Harris and Keble _______ _ x Phyllograptus nobilis Harris and Keble _---------------------------------------­Phyllograptus typus Hall _ ----------------------------------------------· x Pterograptus incertus Harris and Thomas ------------------------------------­Ptilograptus pulmosus (Hall) __ ---------------------------------·--------------------Retiograptus speciosus (Harris)? _____ ------------------------------------------Retiograptus tentaculatus (Hall)? ___ --------_----··-------------------·-Tetragraptus quad ribrachiatus (Hall) --------------------------------------------x Tetragraptus serra (Brongniart) ___ ----------------------------------------------· Trichograptus immotus Harris and Thomas ---------------------------------­Trigonograptus ensiformis (Hall) ---------------------------------------------------x Leperditella sp. . -------------------------------····------------------··-----Paraschmidtella perforata (Harris) -------------------------------------·--------­ ZONE 9 10 x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x Graptolite Faunas, Marathon Region this zone. The lsograpti are represented here by /. forcipi/ormis var. latus and /. ovatus--evolutionary modifications from I. caduceus. Typical assemblages of the second zone can easily be obtained from the Alsate Creek section (measured section XVIII, collections 13, 14, 15, 16, 17, and 149) and from near the highway 1.5 miles south of Marathon, locality 28. Other collections from this zone were made at localities 117 and 152. The zone is approximately 150 to 160 feet thick. The highest 10 to 20 feet of the Fort Peiia formation and the basal 20 to 30 feet of the overlying Woods Hollow shale are characterized by the appearance of more robust biserial scandent rhabdosomes---of which the well-known, long-ranging Glyp· tograptus cf. G. teretiusculus, Amplexo­graptus confertus, and Climacograptus riddellensis are the most common forms. Associated with these species are Amplexo­graptus aff. A. differtus and the last of the Phyllograpti, P. nobilis. Good collections of the typical zonal assemblage were made at localities 85 and 92. King (1937, p. 34) recorded Ceraurus, Bucania, and a rafinesquinoid brachiopod probably allied to Ptychoglyptus from the upper part of the formation near Garden Springs. The writer searched the outcrops around Garden Springs for more specimens of these fossils but none was found. Further, the writer has been unable to lo­cate the original specimens at the U. S. National Museum or at The University of Texas. The paucity of any well· preserved shelly fauna in the Fort Peiia formation precludes a detailed correlation with the Middle Ordovician stages delimited by Cooper (1956). However, R. W. Harris (personal communication) identified Leperditella sp. and Paraschmidtella perforata from the second graptolite zone in the formation and stated that these forms indicate a possible correlation with the Oil Creek limestone of the Simpson group in the Arbuckle Moun· tains. Cooper ( 1956, correlation chart fol· lowing p. 130) placed the Oil Creek lime· stone in the Whiterock stage. The lower and middle parts of the Fort Peiia forma­tion (graptolite zone 8 and at least part of zone 9) are therefore placed in the same stage. Nemagraptus gracilis, which is diag­nostic of Cooper's Porterfield stage, ap­pears 20 to 30 feet above the base of the Woods Hollow shale. The upper part of the Fort Pena formation and the lowest 20 to 30 feet of the Woods Hollow shale prob· ably fall within Cooper's M '1ighly deformed. Because it crops out principally in val· leys, only a few feet of beds are exposed at any one place. In addition to the type local­ity in the Woods Hollow Mountains, good exposures were found on the northeast end of East Bourland Mountain, on Simpson Springs Mountain (Pl. 3, A), in several gullies near the Sunshine Springs thrust, and near the Right Hand Shut Up in the Solitario. The formation consists of greenish­ Bureau of Economic Geology, The University of Texas weathering, black shale with interbedded layers of gray, thinly laminated limestone and tan-weathering, calcareous siltstone, each one-quarter to 1 inch thick, and lenses of yellow-brown weathering conglomerate composed of flattened pebbles of black shale scattered in a gray limestone matrix. The thin beds of limestone and siltstone are more numerous in the basal 60 to 80 feet of the formation. The contact of the Woods Hollow shale and the Fort Pena formation is grada­tional. Where seen, the top 10 feet of the Fort Pena formation is thin-bedded, brown-weathering, gray limestone in lay­ers a few inches thick with interbedded black shale, and the basal 20 feet of the Woods Hollow shale is thin-bedded, brown­weathering, gray limestone in layers up to 2 inches thick and gray shale pebble con­glomerate lenses, both interbedded with greenish-weathering, black shale. At a few localities, principally in the southwestern part of the Marathon basin, the upper 50 to 100 feet of the formation contains scattered, rounded boulders of Early Ordovician and Late Cambrian lime­stone. Baker and Bowman (1917) con­sidered the boulders to be fossiliferous nodules in Late Cambrian and "Ozarkian" shale sequences unconformably underlying the Maravillas chert. They named the beds "Brewster formation" and "Member l" of their "Marathon series." King (1931, p. 1064) recognized that the boulders were exotics in the Woods Hollow shale and abandoned the term "Brewster formation." Ulrich (in Baker and Bowman, 1917) identified faunas from the boulders and established their approximate age. Wilson (1954a) made a detailed study of the boulders and their faunas, and showed that the boulders contain trilobites belonging to the Atlantic as well as the North Amer­ican faunal province. The presence of At­lantic province trilobites suggested to him the possibility of the distribution of Late Cambrian and Tremadoc trilobite faunas from the outer part of the Appalachian trough through the Ouachita geosyncline to the Andean trough following a facies belt. In Wilson's opinion, the blocks slumped off a Middle Ordovician fault scarp and were emplaced in the silty mud of the Woods Hollow formation by violent storms or turbidity currents. Because the blocks of any one rock type include at least one boulder 1 to 2 feet in diameter, a near­by point of origin is indicated. Local, Features Woods Hollow Mountains.-The type locality of the Woods Hollow shale is in an anticlinal valley on the former Louis Granger ranch. Here, the entire formation, 436 feet thick, is clearly exposed overlying the highest beds of the Fort Pena forma· tion, which crop out in the center of the valley. The lower part of the formation is thinly laminated, yellow-brown weather­ing, gray limestone and calcareous silt­stone, each in layers one-half to 1 inch thick, with greenish-weathering, black shale partings. These layers grade up into the characteristic greenish-weathering, black shale with a few interbedded thin layers of gray limestone, siltstone, and shale pebble conglomerate. Four or five thin beds, one-half to 1 inch thick, of coarsely crystalline, gray limestone crowd­ed with comminuted remains of brachio­pods, bryozoa, trilobites, and crinoids oc­cur near the middle part of the formation, and some of the shale beds in the upper part of the formation bear mud cracks. Other loca/,ities.-The upper beds of the formation on the southeast limb of the Dagger Flat anticlinorium and on Simpson Springs Mountain contain more layers of thinly laminated, gray limestone inter­bedded with the black shale. Aside from these minor differences, the Woods Hollow shale is remarkably uniform in lithology, and apparently in thickness, throughout the entire Marathon region. Fossils and Age Graptolites are plentiful in the Woods Hollow shale but are poorly preserved and, because the shale breaks into small pieces, are difficult to collect. The best fossils are preserved along the bedding planes of the Graptolite Faunas, Marathon Region thin limestone and some of the siltstones. Some poorly preserved ostracods were col­lected from the siltstones, and fragments of bryozoa and brachiopods were found in the thin beds of coarse-grained limestone. Although the formation is so highly de­formed that only one complete section was found, enough graptolite collections were made from partial sections so that two and part of a third zone could be delimited in the formation. The following check list gives the zonal distribution of the fossils in the formation. As was discussed under the Fort Pena formation, the basal 30 to 40 feet of the Woods Hollow shale and the upper 10 feet Zonal distribution of species in the Woods Hollow shale SPECIES Amplexograptus confertus (Lapworth) -----------------------------------------­Amplexograptus cf. A. differtus Harris and Thomas -------------------­Amplexograptus cf_ A. perexcavatus (Lapworth) -----------------------­Climacograptus antiquus var. bursifer Elles and Wood ---------------­Cl!macograptus bi~or.nis (Ha!J) -----------------------------------------------------­Chmacograptus ex1mms Rueo,"'lann ---------------------------------------------­Climacograptus modestus Ruedemann -------------------------------------------­Climacograptus modestus var. meridionalis Ruedemann -----------­Climacograptus parvus Hall -------------------------------------------------------------­Climacograptus riddellensis Harris ------------------------------------------------ Climacograptus scharenbergi cf. var. stenostoma Bulman____ _____ _ Corynoides calicularis Nicholson -----------------------------------------------------­Corynoides incurvus Radding ---------------------------------------------------------­Corynoides tricornis Ruedemann ---------------------------------------------------­Cryptograptus tricornis (Carruthers) -------------------------------------------­Dicellograptus divaricatus (Hall) -------------------------------------------------- Dicellograptus divaricatus var. salopiensis Elles and Wood __ _____ _ Dicellograptus gurleyi Lapworth ---------------------------------------------_____ _ Dicellograptus gurleyi var. exilis Ruedemann -------------------------_____ _ Dicellograptus intortus Lapworth ---------------------------------------------·----- Dicellograptus moffatensis var. alabamensis Ruedemann___________ _ Dicellograptus patulosus Lapworth -------------------------------------------------­Dicellograptus sextans (Hall) -------------------------------------------------------­Dicellograptus sextans var. exilis Elles and Wood -----------------------­Dicellograptus smithi Ruedemann ----------·------·-·-------------------------------­Dicranograptus brevicaulis Elles and Wood ----------------------------------Dicranograptus contortus Ruedemann ___ ·----------------------------------------Didymograptus saggiticaulis Gurley ----------------------------------------------­Didymograptus serratulus (Hall) -----------· -----·--------------------------------­Didymograptus subtenu.is (Hall) --------------·-------------------------------------­Diplograptus multidens Elles and Wood _·------------------------------------­Diplograptus multidens var. diminutus Ruedemann -------------------­Glossograptus armatus icholson -----------------------------------------------------­Glossograptus ciliatus Emmons? ------------------------------------------------------Glossograptus hincksii (Hopkinson) _______ ---------------------------·----------Glyptograptus teretiusculus (Risinger) ------------------------------------------Glyptograptus cf. G. teretiusculus (Risinger) ---------------------_______ _ Glyptograptus teretiusculus var. euglyphus (Lapworth) _____ __ ____ _ Glyptograptus teretiusculus var. pygmaeus (Ruedemann) _______ _ Glyptograptus teretiusculus var. siccatus (Elles and Wood) __ ____ _ Hallograptus bimucronatus (Nicholson) ---------------------------------------­Hallograptus mucronatus (Hall) ---------------------------------------------------­Leptograptus flaccidus mut. trentonensis Ruedemann ---------------­Leptograptus validus var. incisus (Lapworth)? ---------------------------­Nemagraptus exilis var. linearis Ruedemann -------------------------------­Nemagraptus gracilis (Hall) -----------------------------------------------------------­Nemagraptus gracilis var. surcularis (Hall) ---------------------------------­Orthograptus calcaratus var. acutus (Lapworth) -------------------------· Orthograptus calcaratus var. alabamensis (Ruedemann) ··---------­Orthograptus whitfieldi (Hall) --------------------------------------------·----------· Retiograptus genitzianus Hall ------------·------------------------------------·-------­Eurychilina papillata Harris ----------------------------------······-------------------­Eurychilina cf. E. subradiata Ulrich -------------·---·--------------·-··------·-···· Schmidtella sp. ----------------------------------------····--·-------------·-·-··--·-----------··-· 10 x x x x ZONE 11 12 x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x A x Bureau of Economic Geology, The University of Texas of the Fort Peiia formation comprise a zone characterized by Glyptograptus cf. G. teretiusculus and Amplexograptus con­fertus. Collections of the typical zone species were made from the Woods Hollow shale at localities 38, 46, and 46A. The first complete zone in the formation is marked by the appearance of the fa­miliar and diagnostic N emagraptus gmcilis and its associates in the genera Nemagrap­tus, Dicellograptus, and Dicranograptus. This zone of N. gracilis is marked by one of the most sudden bursts of new genera in the evolution of the Graptolithina. N. gra­cilis is not common in the zone; however, the zone can easily be recognized by the profusion of Dicellograpti and several species of the genera Dicranograptus, Cryptograptus, and Leptograptus. Diag­nostic species of this zone, in addition to N. gracilis, are N. exilis var. linearis, Lep­tograptus validus var. incisus?, Dicrano­graptus brevicaulis, Dicellograptus mof­fatensis var. alabamensis, and Dicellograp­tus sextans. The Climacograpti and Glypto­grapti, although common in this zone, are overshadowed by the abundance of Dicel­lograpti. N. gracilis and most other species and varieties of the Nemagrapti are re­stricted to this zone. Good collections were obtained from localities 49, 104, 122, 139, and 148. This zone comprises 260 to 280 feet of the formation. The highest graptolite zone in the Woods Hollow shale, that of Climacograptus bi­cornis, is characterized by a continuation of the trend toward larger biserial scan­dent rhabdosomes, and by the widespread development of the well-known Climaco­graptus bicornis. Of the species with large biserial scandent rhabdosomes, Diplo­graptus multidens and Orthograptus cal­caratus var. alabamensis are the most diag­nostic of the zone. The Didymograpti, represented by the long, broad-striped species Didymograptus saggiticaulis and D. serratulus, are seen for the last time in this zone. Good collections of the typical zonal assemblage were obtained from lo­calities 87, 94A, 100, 103, 105, 127, and 136. The upper 150 to 160 feet of the Woods Hollow shale is encompassed by this zone, and all the boulders discussed by Wilson (1954a) are within it. Character­istic zone fossils were collected from the shales surrounding the boulders at Simp­son Springs Mountain and East Bourland Mountain. King (1937, p. 35) reported Diplograp­tus from the lowest beds at the type lo­cality of the formation and the bryozoa Phaenopora, Nicholsonella, Rhinidictya, and Anolotichia, the trilobites Illaenus and Asaphus, the molluscs Modiolopsis and Holopea, and the brachiopod Orthis from higher in the section at the same locality. King ( 1937, p. 36) also recorded Ceraurus, Hormotoma, Dicellograptus, Diplograptus, and Glossograptus from along the road be­tween Ridge Spring and Garden Springs. The writer searched the Woods Hollow shale along the road between Ridge Spring and Garden Springs and all of the outcrops at the type locality for fossils other than graptolites but found only fragments of bryozoa and brachiopods in both localities. Ulrich identified Anolotichia aff. A. revalensis Bassler, Nicholsonella sp., Phae­nopora cf. P. incipiens Ulrich, Stichtopo­rella cf. S. exigua Ulrich, Rhinidictya sp., Sowerbyella ("Plectambonites"} aff. S. quinquecostata (McCoy), Eurychilina sp., and Aparchites sp. from collections made 2 miles southwest of Lightning ranch by Bose (Baker and Bowman, 1917). The writer carefully searched the outcrops of the Woods Hollow shale in that area but was able to obtain only the following ostra­cods: Eurychilina papillata, E. cf. E. sub­radiata, Eurychilina sp., and Schmidtella sp. They came from near the middle of the formation, and R. W. Harris (personal communication) stated that they indicate a correlation with the lower part of the Bro­mide formation of the Simpson group in the Arbuckle Mountains, Oklahoma. Since only fragments of brachiopods were obtained from the Woods Hollow shale, a close correlation with Cooper's ( 1956) stages of the Middle Ordovician is not possible. Cooper does indicate that N emagraptus gracilis and its associates are found in the Porterfield stage. Further, he Graptolite Faunas, Maratlwn Region places the lower part of the Bromide for­mation in that stage. Thus the basal beds of the Woods Hollow shale, those older than the zone of N. gracilis, are older than the Porterfield stage and fall within the Ashby stage. The zone of N. gracilis and possibly part of the overlying C. bicornis zone fall within the Porterfield stage. At least part of the C. bicornis zone probably is within the lower part of the Wilderness stage. The next younger zone in the Marathon se­quence, that of Orthograptus truncatus var. intermedius, is a correlative of the basal part of the Viola limestone in the Arbuckle Mountains. Since Cooper places the basal part of the Viola limestone in the upper part of the Wilderness stage, a part, only, of the C. bicornis zone is placed in the lower part of that stage. MARA VILLAS CHERT General Features Baker and Bowman (1917, p. 87) named the Maravillas chert for its exposures at Maravillas Gap, 20 miles southwest of Marathon. It crops out on the inner slopes of the novaculite-capped ridges that are so characteristic of the Marathon region. Its black cherts and limestones stand out in marked contrast to the white novaculite above them. Good exposures are present in the cliffs that rise above the swimming pool at the Picnic Grounds 5 miles southwest of Marathon, at Rock House Gap located at the southwestern end of the southeast limb of the Marathon anticlinorium, and on the northwest slope of Threemile Hill, 314 miles northeast of Maravillas Gap (Pl. 1). The formation is composed of layers of black chert 6 to 8 inches thick alternating with light-gray weathering, black, petro­liferous limestone layers 4 to 8 inches thick (Pl. 3, B). Also, it includes some inter­bedded lenses of chert and limestone peb­ble conglomerate, a few thin, pink-weather­ing shale partings, and a few layers of sub­graywacke 4 to 6 inches thick, some of which exhibit graded bedding. Both the black chert and the limestone are lenticular and intergrade along strike. Black chert predominates over limestone in the upper 150 to 200 feet of the formation, but the difference is not sufficient to warrant sep­aration of this part as a distinct member. The rocks of the Maravillas chert reflect a sharp change in the sedimentary en­vironment. The chert and limestones over­lie the Woods Hollow shale conformably, and although a coarse conglomerate is found at the base of the Maravillas chert in some places, paleontologic evidence has not revealed any considerable temporal break between the two formations. The Maravillas chert ranges in thickness from 200 to 250 feet in the Marathon anti­clinorium; it thickens southeastward to about 350 feet on the northwest limb of the Dagger Flat anticlinorium and is nearly 400 feet thick on the southeast limb. It apparently thins farther to the south, because it is about 200 feet thick in the old Jones ranch area and about the same thickness in the Solitario. Local Features Maratlwn anticlinorium.-The upper­most 5 feet of the formation exposed in the ridge trending northeast from the swim­ming pool is composed of interbedded pink. weathering shale and chert in layers half an inch to 3 inches thick. The shale con­tains latest Ordovician graptolites. Similar graptolites have been obtained from lime­stones at the top of the formation in several localities. Because of the contained fossils and the resemblance of the pink-weather­ing shale to shale partings in the middle part of the Maravillas chert, the shales are included in the Maravillas formation and are not referred to a younger formation as suggested by Wilson (1954b, p. 2470). The lower 50 feet of the formation includes numerous beds of chert and limestone peb­ble conglomerate (the pebbles range in size from one-eighth inch to about 2 inches in diameter) which contain fragments of bryozoa and trilobites. A basal conglomerate about 10 feet thick is exposed at Rock House Gap. Black chert and black limestone pebbles are common Bureau of Economic Geology, The University of Texas in the conglomerate, but it also includes stone in beds 2 to 4 inches thick inter· rock types not found in the Marathon re­bedded with the black chert. gion, such as a brownish, medium-grained, quartzose sandstone and pinkish dolomite. Fossils and Age Abraded remains of corals are present in the coarse-grained, brown, quartz sand matrix. The conglomerate is a lens and passes into black chert along strike. Dagger Flat anticlinorium.-At Three· mile Hill and at the type locality, Mara. villas Gap, the Maravillas chert is bounded at its base by the major fault plane of the Threemile Hill thrust. Near the middle of the section at both of these localities sev· eral beds of coarse-grained calcarenite 2 to 10 feet thick contain abundant frag· ments of bryozoa and trilobites. Similar coarse-grained calcarenite beds, but thin· ner and less fossiliferous, crop out near the middle of the formation on the southeast flank of the Dagger Flat anticlinorium north from Threemile Hill. Southern exposures.-Chert predomi· nates over limestone in all exposures south 0£ the Marathon basin. On Rough Creek, in the Dove Mountain quadrangle, the for. mation consists of black chert in layers 3 to 10 inches thick with a few interbedded layers of black limestone 4 to 6 inches thick. In the old Jones ranch area and at Persimmon Gap, the entrance to Big Bend National Park on State Highway 51, the upper 20 to 40 feet of the formation con­sists of black chert in layers 4 to 10 inches thick; whereas lowei:: in the section, black chert, black limestone, and a few chert and limestone pebble conglomerate lenses are interbedded. In the several exposures of the formation along the northeastern front of the Santiago Mountains, the formation consists of interbedded layers of black chert 4 to 8 inches thick and a black lime­stone 4 to 6 inches thick. At the Right Hand Shut Up in the Solitario, 154 feet of the formation is exposed in a section that has been intruded by sills. Here it is nearly all black chert with only a few black limestone lenses, but other outcrops of the formation in the Solitario include some black lime· Fragments of fossils are present through· out the Maravillas chert, but the preserva. tion is so poor that identification is diffi. cult. Graptolites have been collected f~om the limestones in all parts of the formation. The conglomerates at the base of it have yielded abraded remains of . cor.als and brachiopods. Fragments of trilobites and ostracods were collected from the black fine·grained limestones, some of the lime· stone pebble conglomerates, and from the coarse-grained calcarenite beds that are crowded with bryozoa. In addition to sev· eral species of bryozoa and a few trilobites and ostracods, these beds have also yielded brachiopods and corals. Scattered through the black cherts are sponge spicules and some Radiolaria, but no attempt has been made to classify these fossils. Enough grap· tolites have been collected from the lime· stones to identify three zones in the forma· tion. The following check list (p. 29) gives the zonal distribution of fossils in the £or· ma ti on. The lowest zone is characterized by the appearance of large Orthograpti, the fol. lowing species 0£ which are typical: Ortho· graptus truncatus var. intermedius, 0. quadrimucronatus var. angustus, 0. quad· rimucronatus var. cornutus, and 0. calca· ratus var. incisus. Climacograptus typicalis var. crassimarginaUs and Dicranograptus nicholsoni are two other species that are common. The trilobites Cryptolithus and Ampyxina and the coral Streptelasma were collected from the basal beds of the zone. Collections of the typical zonal assemblage were made at localities 73, 86B, 128, 133, 134, 134A, and 135. King (1937, p. 41) recorded Colum· naria, Halysites, Paleofavosites, Strepte· lasma, Platystrophia, and Hebertella from the basal conglomerate of the Maravillas chert at Rock House Gap. From limestones overlying the conglomerate, he obtained Cryptolithus, Harpes, Strophomena, Cli. Grapwlite Faunas, Marathon Region Zonal distribution of species in th e Maravillas chert ZONE SPECIES 13 14 15 Climacograptus antiquus Lapworth ----------------------------------------------· x Climacograptus caudatus Lapworth ___ ---------------------x x Climacograptus hastatus T. S. Hall ----------------------------------------------­x Climacograptus minimus (Carruthers) -----------------------.. ----------­x Climacograptus mississippiensis Ruedemann -----------------------------x Climacograptus putillus (Hall) ___ ----------------------------------x Climacograptus scalaris var. miserabilis Elles and Wood? x Climacograptus scharenbergi Lapworth _ ____ -------------------x Climacograptus spiniferus Ruedemann __ -----------------------------···------­x Climacograptus tubuliferus Lapworth -------------------------------------------­x Climacograptus typicalis Hall ----------------------------·--------------­x x Climacograptus typicalis var. crassimarginalis Ruedemann and Decker ________ ----------------------------------x Climacograptus cf. C. ulrichi Ruedemann ------------------------------------·­x Dicellograptus complanatus Lapworth .... -----------------------·-------------·-x Dicellograptus complanatus var. arkansasensis Ruedemann ____ _ x Dicellograptus complanatus var. ornatus Elles and Wood------------x Dicellograptus forchammeri (Geinitz)? _________ ------·-----·-------x Dicellograptus forchammeri var. flexuosus Lapworth __ _ x Dicellograptus pumilus Lapworth ... -----------------·----x Dicranograptus nicholsoni Hopkinson ______ .................... x Dicranograptus nicholsoni var. geniculatus Ruedemann and Decker --------------------------------·---·-----------------·---·--­x Diplograptus crassitestus Ruedemann ---------------------·---·-­x Diplograptus minutus Berry, n.sp. --------------------·---------·-·------------------· x Leptograptus annectans (Walcott) ----------------------------------------·-----·--· x Orthograptus calcaratus (Lapworth) ? ----------·------------------------------· x Orthograptus cf. 0. calcaratus var. basilicus Lapworth __ _ x Orthograptus calcaratus var. incisus (Lapworth) ........................ x Orthograptus cf. 0. calcaratus var. vulgatus (Lapworth) ·--------· x x Orthograptus quadrimucronatus (Hall) _______ ................................. x Orthograptus quadrimucronatus var. angustus (Ruedemann) ___ _ x Orthograptus quadrimucronatus var. cornutus (Ruedemann) ___ _ x Orthograptus aff. 0 . truncatus (Lapworth) -----·------·--------x x Orthograptus truncatus var. abbreviatus (Elles and Wood)? __ _ x Orthograptus truncatus var. intermedius (Elles and Wood) ____ __ x Orthograptus truncatus var. pertenuis (Ruedemann) ...... x x Orthograptus truncatus var. recurrens (Ruedemann) . x Orthograptus truncatus var. socialis (Lapworth) ........... . x Retiograptus deckeri Ruedemann . x Retiograptus pulcherrimus Keble and Harris .............................. x x Cryptolithus sp. ________________________________________ -----------------x x Ampyxina sp. ---·-·-------------·-................... x Flexicalemene sp. ·-·-------------------------------------------· x Hallopora sp. .......................................................___ _ x Helopora sp. -----·--·--------·--------·----·--·--·-----·---·---------------------------·-··--------x Christiana? sp. ------------···-·--·----------·------------------··------------··----·-··--·------·· x Paterula sp. ......................................................................................... x Streptelasma sp. --·---------------------------------------------------------------x Zygospira sp. ----·-......................................................... .. )( macograptus antiquus, Diplograptus am­this collection at the U. S. National Mu­plexicaulis, and "Dicellograptus" nichol· seum and confirms the identification of soni. The last-named form must be a mis­Diplograptus amplexicaulis (Orthograp­print since there is no species "nicholsoni" tus ail. 0. truncatus herein), Aparchites of the genus Dicellograptus. In the genus sp., Eurychilina, and Cryptolithus. Cooper Dicranograptus, however, "nicholsoni" is (personal communication) identified an a well-known species and is characteristic immature Christiana? and Paterula from of this horizon. King (1937, p. 41) records this collection. King (1937, p. 41) lists a a list of ostracods, brachiopods, a trilobite, few graptolites which Ruedemann identi­and a graptolite identified by Ulrich from fied from three localities north of the collections made by Baker and Bowman at town of Marathon. Rock House Gap. The writer re-examined The second zone in the Maravillas chert Bureau of Economic Geology, The University of Texas is characterized by several species of large Orthograpti associated with large Dicello­grapti. Orthograptus quadrimucronatus (the typical form) is the most widespread and diagnostic species of this zone. Other characteristic species include Climaco­graptus tubuliferus, Dicellograptus for· chammeri?, Orthograptus cf. 0 . calcaratus var. vulgatus, and Orthograptus aff. 0. truncatus. The trilobites Flexicalymene and Cryptolithus and the bryozoa Hallopora were identified in collections made within this zone at Threemile Hill. Collections of the typical zone species were obtained from localities 45, 55, 83A, 86A, and 132. King (1937, p. 41) reproduced from Baker and Bowman (1917, pp. 89-90) a list of bryozoa and brachiopods which they collected at Maravillas Gap and which UJ. rich identified. Baker and Bowman ( 1917, p. 90) added a second list of corals and brachiopods. King (1937, p. 41) stated that the calcarenite lenses composed of bryozoa and other fossils found in the mid­dle part of the Maravillas chert in the southern part of the Marathon uplift are "built of such genera as Constellaria and Pachydictya, in which are imbedded a few shells of Platystrophia, Rafinesquina, Hebertella." The writer searched the Mara­villas chert at Maravillas Gap for bryozoa and brachiopod material similar to that collected by Baker and Bowman but was able to find only some poorly preserved specimens. Further, the writer was unable to locate the original collection on which Ulrich worked at the U.S. National Mu­seum. The bryozoan calcarenite beds from which the writer collected at Threemile Hill are in the second zone in the Mara­villas chert. The third zone in the formation is char­acterized by Dicellograptus complanatus and its varieties, by three small species of Climacograptus, and by Diplograptus cras­sitestus. The Orthograpti are represented by two small varieties of Orthograptus truncatus-0. truncatus var. socialis and 0. truncatus var. abbreviatus?. A form like the typically lower Silurian species Clima­cograptus scalaris var. miserabilis was found here also. Good collections of the typical species of the zone were obtained from localities 60, 138, and 147. The zone is about 50 feet thick. The writer found no fossils other than graptolites in the upper 100 feet of the Maravillas chert. These beds are composed predominantly of chert; however, Bassler (1950, p. 19) listed five species of corals characteristic of the Richmond stage from the Maravillas chert but gave neither stra­tigraphic nor locality data. The age of the Maravillas chert has been the subject of considerable discussion. Schuchert (in Udden, 1907) considered the first fossils found in the chert-limestone sequence to be of Trenton age. Ulrich (in Baker and Bowman, 1917) considered the lower part of the Maravillas chert to be correlative with the middle and upper part of the Viola limestone in the Arbuckle Mountains and the Trenton limestone of New York, because he regarded the fossils Baker and Bowman collected from the base of the formation at Rock House Gap to he of Trenton age. Further, he stated that the fauna of bryozoa and brachiopods from Maravillas Gap was a "typical Fernvale­Richmond fauna," and he considered that the upper part of the formation had a simi­lar relation to the Trenton part as the Fern· vale-Richmond zone had to the Viola lime­stone in Oklahoma. Ulrich thought that the Fernvale-Richmond zone and its cor­relatives marked a great transgression fol­lowing a period of emergence and placed it at the base of the Silurian. Thus Ulrich divided the Maravillas chert (as he did other western formations such as the Mon· toya limestone and Bighorn dolomite) into a lower part correlated with the Trenton and an upper part correlated with the Fernvale-Richmond. Kirk (1930, p. 465) gave his opinion that the "Cryptolithus zone" of the Mara­villas chert was probably of Cincinnatian age. He used Cincinnatian in the sense of pre-Richmond and post-Trenton. King (1937, p. 41) reported that Kirk had col­lected Cryptolithus from the "reef beds on Threemile Hill." Fragments of this trilobite Graptolite Faunas, Marathon Region are abundant in the calcarenite beds com­posed of bryozoa and other organisms at Threemile Hill, and, as discussed above, these beds fall within the second graptolite zone in the formation. King ( 1931, p. 1075; 1937, pp. 41-42) assigned Late Ordovician age to the Mara villas chert, and it is placed in the Richmond stage in the Ordovician correlation chart (Twenhofel et al., 1954). The graptolite fauna of the formation displays a gradual change so that three zones are recognized. The discussion of the age of the formation involves the grapto­lites principally, because the other fossils are too poorly preserved and are not found at regular enough intervals to be useful for detailed work. The fauna of the Denmark limestone of the type Trenton includes the graptolite species Orthograptus truncatus var. inter­ medius which is the most characteristic species of the lowest graptolite zone in the Maravillas chert. The writer examined Ruedemann's collections at the New York State Museum in Albany and recognized this species from the Denmark limestone only. It had not been collected from the lower beds of the Trenton stage. The writer examined Decker's collec­tions from the Viola limestone which are at the University of Oklahoma. The follow­ing species were recognized from collec­tions made near the base of the formation: Dicellograptus /orchammeri var. flexuosus, Dicranograptus nicholsoni, Climacograp­tus typicali,s var. crassimarginalis, Ortho­graptus truncatus var. intermedius, and Orthograptus quadrimucronatus var. spini­gerus. Four of these species are common to both the basal part of the Viola limestone and the lowest zone of the Maravillas chert, including the diagnostic 0. truncatus var. intermedius. The lowest zone in the Maravillas chert, the lower part of the Viola limestone, and the Denmark lime­stone in the type Trenton are considered correlatives. Because Cooper ( 1956) placed the base of the Viola limestone in the upper part of the Wilderness stage, the base of the Maravillas chert is placed in the same part of this stage. The graptolite fauna of the second zone in the Maravillas chert can be correlated with the graptolite fauna of the Lorraine group in New York. The most diagnostic species are Orthograptus quadrimucrona­tus and Climacograptus typicalis which are common in both the Maravillas chert and in the Lorraine group. Climacograptus typicalis is also found in the Southgate formation of the Eden group in Cincinnati. The Lorraine group was correlated with the Eden and part of the Maysville by Ruedemann (1925a) and this correlation was followed in the Ordovician correlation chart (Twenhofel et al., 1954) . Zone 2 in the Maravillas chert is correlated with the Eden and Maysville stages. The Crypto­lithus zone mentioned by Kirk (1930, p. 465) is in zone 2, and the writer agrees with the Cincinnatian age proposed by Kirk for the particular part of the forma­tion in which he found the fragments of Cryptolithus so abundant. The graptolite fauna of the third zone in the Maravillas chert is correlative with the highest Ordovician graptolites in the Eng­lish and Australian sequences. Since the zone is evidently post-Maysville and latest Ordovician in age, it must be Richmond, although the type Richmond has but three little-known graptolites. Also, the Sylvan shale in Oklahoma has a fauna very similar to the third zone and it is placed in the Richmond stage in the Ordovician correla­tion chart (Twenhofel et al., 1954). The Maravillas chert represents late Middle Ordovician and all of Late Ordovician time. The original diagnosis by Ulrich of a Trenton fauna and a Richmond fauna in the formation is correct, but the Eden and Maysville are also represented. There is no break in time within the Maravillas chert; there seems to have been continuous dep­osition from late Wilderness time through the Trenton and all of the Late Ordovician. Bureau of Ecorwmic Geology, The University of Texas DEPOSITIONAL HISTORY OF THE ORDOVICIAN STRATA From a consideration of the rock types and their planktonic fauna-graptolites­a few conclusions concerning the con­ditions of deposition may be inferred. The Marathon limestone includes calci­lutite, current-laminated bed~ of fine­grained calcarenite, shale, many con­glomerate lenses, and some subgraywacke lenses. These subgraywackes, like those higher in the succession, are composed of grains of quartz, plagioclase, sericite, and glauconite, and fragments of calcarenite. The cementing material is predominantly calcite. The source of the elastic material doubtless lay to the south, because areas to the west, north, and east were sites of carbonate deposition during Early Ordovician time. Also, the formation includes more shale and thicker subgray­wacke layers in its more southerly expo­sures (the old Jones ranch and Solitario areas) than it does in the main uplifts. The dip of the cross-lamination in the calcare­nite layers indicates the last current acting came from the southwest. This current may have been a longshore current operating at an angle to the actual direction from which the sediment came. For a short period in the middle part of Early Ordovician time, patch reefs grew extensively in the area of the present Mara­thon anticlinorium and to a lesser extent in the Dagger Flat anticlinorium area. These oval lenses, composed of calcilutite surrounded by a network of dolomite, char­acterize the Monument Spring dolomite member and contain a different fauna from the surrounding rocks. The reef masses were probably built up by algae which acted as trappers and binders of bioclastic lime debris. Cup-shaped sponges were sec­ondary parts of the framework-forming widely spaced tie points between which the algae grew. In and around this mass, gas­tropods, nautiloids, and brachiopods flour­ished. The reef masses were small mounds and doubtless resembled in size and pos­sibly in shape small patch reefs found in the lagoons of many modern coral atolls. They probably grew during a period of quiescence when the larvae of bottom­ dwelling organisms floated into the re­ gion and were able to settle and grow successfully on the sea floor. After a time, wave action increased and coarser-grained sediment went into suspension and washed around and over the reefs, ending their growth. Some of the calcarenites in the forma­ tion are penetrated by small tubes filled with comminuted material, perhaps left by a burrowing animal. Also, a few of the calcareous shale layers bear mud cracks. These features, in addition to the reefs, the intraformational conglomerate, the cross­ lamination, and the pellet and aggregate structures in the calcilutites, indicate that the Marathon limestone was deposited in an area covered by shallow water subjected to wave and current action and which, at least in places, was temporarily exposed and became a mud flat. The area appears to have been a shelf, possibly with some local highs. A land mass lay to the south; it contributed only a little noncalcareous material to the northern part of the region but a considerable amount to the southern part. Carbonate formation ceased during dep­osition of the Alsate black shale in the areas of the present main uplifts and of the Rodriquez Tank quartzose s11ndstone in the old Jones ranch and Solitario areas. Although the sandstone is exposed only in two areas, it is very similar in both and may well have been a continuous near­shore deposit. Possibly an uplift had oc­curred to the south so that the shore line was near the present sites of the Solitario and old Jones ranch. A relatively small amount of fine-grained sediment was carried to the northern part of the Mara­thon region. The present Marathon basin was occupied by a stable water mass and reducing conditions prevailed. Black sh~le deposition was 11pparently of short durat10n; then carbonate deposition returned. The rocks of the Fort Pena formation consist of alternating layers of medium-and fine-grained, cross-laminated Grapwlite Faunas, Marathon Regi,on calcarenite, chert composed of radiating fibers of chalcedony, black shale, and lenses of subgraywacke and chert and lime­stone pebble conglomerate. The dip of the current laminae indicates that the last cur­rent to pass over the calcarenite beds came from the southwest. Also, several beds with biserial graptolites arranged with their long axes subparallel were found near the top of the formation. The proximal (nar­row) ends of the rhabdosomes point S. 25° W. to S. 40° W., indicating that the last current to pass over these rhabdosomes came from the southwest. As indicated above, the cross-laminated calcarenite layers were probably deposited above wave base in shallow water. The calcarenites of the Fort Pena forma­tion become more thinly laminated near the top and grade into the thinly laminated fine-grained calcarenites and the shales of the overlying Woods Hollow formation. The environment in the depositional area slowly changed to one in which mud was being deposited. Currents periodically swept different material into the area of black mud accumulation. In some cases, the currents carried fine sand-sized grains of calcite and in other cases, silt and fine sand-sized quartz grains. In some places, the currents ripped fragments of shale from the bottom and incorporated the frag­ments with the material they were carrying. Nearly all the fossils found in the forma­tion came from the siltstone and calcare­nites. The fossils are poorly preserved­showing signs of transport. The graptolites with biserial rhabdosomes are commonly aligned with their proximal ends pointing southwest. Some of the shale layers bear mud cracks, and the presence of them indi­cates that the water became shallow in the Marathon region during the time of depo· sition of the Woods Hollow shale. From time to time, parts of the area were tempo­rarily exposed. The presence of mud cracks is at present considered good evidence of shallow water. However, subaqueous shrinkage cracks are a possibility, although their formation in a layer has not been demonstrated (Pettijohn, 1957, p. 193). The region may have been a large mud flat across which water fluctuated and into which silt and sand-sized material was carried periodically by currents generated by storms. The exotic boulders described by Wilson ( l 954a) occur in the upper 15 to 70 feet of the Woods Hollow shale. The boulders are slabs with rounded corners and are composed of several types of limestone not found in the Marathon region. They range from several inches to 10 feet in length and are found in a rather restricted area on the southwest side of the Marathon basin. The shale around the slabs is in­tensely contorted, and the slabs occur as isolated masses. Fragments of other ma­terials are not present. The slabs were probably derived from a rising highland, possibly to the west, and the processes which produced them may have been re­lated to the general disturbances which af­fected much of the geosynclinal area in eastern North America during the latter part of the Middle Ordovician. The black limestones and cherts of the Maravillas chert represent a change in the sedimentary environment in the Marathon region. The formation is com· posed of interbedded chert, composed of a fine-textured mass of cryptocrystalline quartz, and calcilutite with some lenses of intraformational conglomerate, subgray· warke, and pinkish-weathering shale. The black silica and lime muds could be the product of reducing conditions either in the water mass or below the water­sediment interface. When such conditions prevail below the interface, rapid sedi­mentation is taking place to prevent oxy­genation of the sediment. The absence of a bottom-dwelling fauna and the fact that the 200 to 400 feet of sediment now compris­ing the Maravillas chert was deposited dur­ing a long period of time (from late Middle Ordovician through Latest Ordovician) , indicate that the reducing environment was above the water-sediment interface. A stable water mass persisted over the bottom of the present Marathon region throughout the time during which the rocks of the Bureau of Economic Geology, The University of Texas Maravillas chert were being deposited. The water may have been either shallow or deep; however, it was shallow enough so that the bryozoa, trilobites, and corals, which now form coarse-grained calcarenite beds, could thrive in local patches. These patches were areas of the sea floor where water circulation was sufficient to over­come the reducing conditions temporarily and permit growth of the bottom-dwelling organisms. The areas were local in extent and the bottom-dwelling fauna flourished for a short time and then was overcome by toxic water from adjacent areas. Also, cur­rents ripped limestone and chert pebbles from the sea floor and incorporated them into conglomerates from time to time. Fine-grained deposits of calcium carbon­ate and silica slowly accumulated in the re­ducing environment. A nearby land mass was probably the source for the quartz and feldspar in the subgraywacke lenses. Because of the freshness of the feldspar in the subgraywacke, such a land mass does not seem to have undergone enough chemi­cal activity to supply silica only. Thus it probably was not the source of colloidal silica as King (1937, p. 46) postulated. Sediments similar to those in the Marathon region were being deposited northwest of it. Limestone was being de­posited for several hundred miles north­ward. Therefore, there does not appear to have been a suitable source for silica in the colloidal form. Graptolite-bearing rocks may be either deep or shallow-water deposits (Bulman, 1955, pp. Vl6-Vl7). From a study of the Ordovician strata in the Marathon region, a shallow-water origin may be postulated for the lower and middle parts of the suc­cession, but evidence is inconclusive for the upper part. During much of the time of deposition of the Ordovician succession, the bottom was foul and probably the waters were turbid. These conditions are unfavorable to the growth of a bottom­dwelling fauna. Thus graptolites-pelagic organisms-and a few inarticulate bra­chiopods that could withstand a wide vari­ation in environmental conditions are found as the principal fossils. Only during the development of the reef patches in the middle part of Early Ordovician time and the bryozoa in the middle part of Late Ordovician time, were bottom-dwelling or­ganisms able to thrive in any part of the Marathon region. DEVONIAN SYSTEM Overlying the Maravillas chert is a se­quence of white novaculites and vari­colored cherts and shales. This sequence was named the Caballos novaculite by Baker and Bowman (1917, p. 93) who designated Horse Mountain as the type locality. King (1937), after a detailed study of the formation, divided it into five members. The writer and Nielsen (1958) discussed the regional aspect of the mem· hers and showed that the lowest member­a brown chert--overlies the Maravillas black cherts and limestones in the Mara­thon basin. In the Solitario, old Jones ranch, and Persimmon Gap exposures, the pink shales of King's third member overlie the Maravillas chert. Graves (1952) des­cribed conodonts from the upper part of the Caballos novaculite and interpreted the fauna to be of Late Devonian age. CORRELATION CORRELATION WITHIN NORTH AMERICA The details of the fauna found in each formation have been discussed. Graptolites are plentiful throughout the sequence and 15 zones have been delimited. Although other elements of the fauna are few, and recent detailed work on the graptolite­bearing rocks in other regions is lacking, some correlations can be made (table 2). Good correlation is possible with the well­known Ordovician graptolite-bearing rocks of Quebec and New York. A few fossils only have been collected from the Schaghticoke shale in New York, but the presence of Dictyonema canadense (Bulman, l 950a, p. 72) , Staurograptus dichotomus var. apertus, and Bryograptus patens in this shale and in the Matane shale of Quebec indicates similarity in age be­tween these two formations. The Matane shale contains a more varied graptolite fauna (Bulman, 1950a), including species of Anisograptus and Triograptus. These latter two genera and the genus Stauro­graptus are represented in zone 1 of the Marathon sequence and indicate a probable correlation between this zone and the Matane shale. Thus the lowest zone of the Marathon succession, the Matane shale of Quebec, and the Schaghticoke shale of New York are considered correlatives. The Clonograptus-Adelograptus assem­blage which characterizes zone 2 of the Marathon sequence has been recorded from but one other locality in North America. Kindle and Whittington (1958, p. 331) have collected the typical zonal assemblage from western Newfoundland. The correlation between the Marathon limestone and the standard Lower Ordovi­cian section has been discussed above under the heading "Fossils and age of the Mara­thon limestone" (pp. 15-19). As was pointed out in that discussion, the presence of Bellefontia in zone 1 and Ophileta, etc., in zone 2 suggests that zone 1 and at least part of zone 2 may be correlated with the Gasconade dolomite of this standard section. Raymond's ( 1914) zone A of the Levis shale and zone 3 of the Marathon sequence have similar faunas, the following species being common to both: Clonograptus fiexilis, Clonograptus rigi.dus, T etragraptus approximatus, T etragraptus quadribra­chiatus, and T etragraptus serra. Of these species, T. approximatus, which is con· fined to zone 3 in the Marathon succes· sion, is the most characteristic form in both areas. The fauna of the Monument Spring dolomite member, which as discussed earlier (p. 17) lies within zone 3, can be correlated with the Rich Fountain forma­tion in the standard Lower Ordovician sec­tion for the United States and with the middle part of the Kindblade formation in the Arbuckle Mountains. Raymond's (1914) zones B, C-1, and C-2 of the Levis shale and Ruedemann's (1902) zone 1 and zone 2, bed 1, of the Deepkill shale contain many of the same species as zones 4, 5, and 6 of the Marathon succession. The writer has seen the diag­nostic forms of Tetragraptus fruticosus ( 4-branched and 3-branched varieties) in collections from the Levis and Deepkill shales, and thus this species has been col­lected from all three areas. Zone 1 of the Deepkill section and zone 4 of the Mara­thon section have 12 species common to both. Miser and Purdue (1929, p. 27-28) listed an assemblage of graptolites from the Mazarn shale that are common in zone 4 of the Marathon limestone. This collec­tion is the oldest obtained from the Ordo­vician section of the Ouachita Mountains. Two of the underlying formations, the Crystal Mountain sandstone and the Collier shale, have arbitrarily been included in the Ordovician system. The Collier shale has yielded indeterminate fragments which may be graptolites but no age determina­tion is possible. Di.dymograptus protobifidus, the diag­nostic species in zone 6 in the Marathon Table 2. Correlation of graptolite-bearing sequences in North America Stages GRAPTOLITE ZONES MARATHON OUACIIlTAS AR BUCKLES Ric hmond 15. D. complanatus Polk Creek Sylvan Fernvale -­ May Ede1 sville n 14. 0. quadrimucronatus Maravillas Bigfork Viola -- Trennton -­ 13. 0. truncatus var. intermedius Wilederness 12. C. bicornis Womble Bromide -­ Woods Portterfield 11. N. gracilis Hollow -­ Tulip Creek AshIby 10. G. cf. G. teretiusculus McLish Marmor Fort -­ Pena 9. H. etheridgei -- Whi terock 8. I. caduceus Alsate Blakely Oil Creek 7. D. bifidus Joins ·-­ z -< ~...... i:.:18 i1<:> °" 0 ::Jo ~ 0 z < -t1 >0 0 ~ 0 i:£I .....< 0 0 - :::s z -< u ­ 0> 0 ~ 0 ~ i:£I e:: 0 .....< Stages not y t e: tab-Ji hed - 6. D. protobifidus 5. T. fruticosus (3-br. and 4-br.) I 4. T. fruticosus ( 4-br.) 3. T. approximatus 2. Clonograptus 1. Anisograptus Marathon Mazarn Crystal Mountain Collier NEW YORK QUEBEC Queens ton Oswego Lorraine group Upper Utica Loyal Creek Nowadaga Magog Canajoharie N ormanskill I I I I Deep kill Levis (Zone 3) (Zone D) I I I I I I I West Spring; Deep kill Levis Creek (Zones 1-2) (Zones A-C) Kindblade Cool Creek McKenzie Schaghticoke MataneHill Grapwlite Faunas, Marathon Region succession, is known from the West Spring Creek formation in the Arbuckle Moun­tains and from the Smithville limestone of the standard Lower Ordovician section. Since D. protobifidus is limited to zone 6, that zone, the Smithville limestone, and the West Spring Creek formation are con­sidered correlatives. The graptolite assemblage which is characteristic of zone 7 of the Marathon sequence has been recorded by Raymond (1914) from zone C-3 of the Levis shale and by Ruedemann (1902) from zone 2, bed 2, of the Deepkill shale. The diagnostic species of zone 7, Didymograptus bifidus, has been found in all three areas. Further, eight identical species have been found in the Deepkill shale and zone 7 of the Mara­thon limestone, and four species are com­mon to both zone C-3 of the Levis shale and zone 7 of the Marathon limestone. The diagnostic species of the zone, Didymo­graptus bifidus and D. artus, have been collected from the Joins formation in the Arbuckle Mountains and from the Black Rock limestone of the standard Lower Ordovician section (Ruedemann, 1947, pp. 326-327) . As has been pointed out above, Cooper (1956) has placed the Joins formation in the early Middle Ordovician. Therefore, its correlatives, the Black Rock limestone and zone 7 of the Marathon lime­stone, would also be early Middle Ordovi­cian in age. Raymond's (1914) zone D of the Levis shale and Ruedemann's zone 3 of the Deep­kill shale each contain two species-Tetra­graptus quadribrachiatus and Trigono­graptus ensiformis-found in zone 8 in the Fort Pefia formation in the Marathon re­gion. Both of these species range into zone 9 in the Marathon sequence, and, in addition, three species found only in zone 9 are found in zone D of the Levis shale and five species restricted to zone 9 are in zone 3 of the Deepkill shale. Thus, zone D of the Levis shale and zone 3 of the Deep­kill shale are tentatively correlated with zone 9 only, of the Marathon region. Miser and Purdue ( 1929) list species of the genera Didymograptus, Glossograptus, Glypwgraptus, and lsograptus from the Blakely sandstone, and Ruedemann (1947, pp. 95-96) listed two faunas from ex­posures of that formation near Hot Springs, Arkansas. One list included Loganograptus logani, I sograptus caduceus var. nanus, and Didymograptus euodus. The presence of /. caduceus in the for­mation indicates a probable correlation with zone 8 of the Marathon sequence. The second list included Climacograptus pun­gens, Glyptograptus dentatus, Glossograp· tus horridus, and Glossograptus hystrix. These forms indicate a probable correlation with zone 9 of the Marathon succession. Thus the Blakely sandstone is correlated with the Alsate shale and with most of the Fort Pefia formation. A few ostracods were collected from the upper part of the Fort Pefia formation, zone 9. R. W. Harris (personal communication) identified Lep­erditella sp. and Paraschmidtella perforata (Harris) in a collection from this zone and stated that they indicate a correlation with the Oil Creek formation of the Simpson group in the Arbuckle Mountains. M. E. Upson, of Gulf Oil Corporation (personal communication), has identified ostracods from the upper part of the Fort Pefia for­mation which are typical of the McLish formation of the Simpson group and ostra­cods from the Woods Hollow shale which are typical of the Tulip Creek formation of the Simpson group. The ostracods typical of the Tulip Creek formation came from graptolite zone 11 which is in the Woods Hollow shale. Thus graptolite zone 10 and possibly part of zone 9 are correlatives of the McLish formation, and at least part of graptolite zone 11 is a correlative of the Tulip Creek formation. Graptolite zones 11 and 12 have a dis­tinctive fauna that includes several species in common with the Normanskill shale of New York and the lower and middle parts of the Womble shale in the Ouachita Mountains. Also, Decker (1952) has re­corded many occurrences of the typical as­semblages of zones 11 and 12 in his discus­sion of the "Athens" shale. Ostracods char­acteristic of the lower part of the Bromide Bureau of Economic Geology, The University of Texas formation of the Simpson group in the Ar­buckle Mountains were collected from the middle part of the Woods Hollow shale, which is in graptolit~ zone 11 (zone of N. gracilis) . Cooper ( 1956) correlated the Bromide formation with the lower and middle parts of the Womble shale. Since, using graptolites, the Woods Hollow shale and the lower and middle parts of the Womble shale may be correlated, the Woods Hollow shale, the lower and middle parts of the Womble shale, and the Bro­mide formation are considered correlative. The writer examined Decker's collections from the Bigfork chert and the Viola lime· stone at Oklahoma University, and Ruede­mann's collection from the Snake Hill, Canajoharie, Utica, Deer River, and At­water Creek shales and from the Lorraine group at the New York State Museum. The assemblage of large orthograptids which characterizes graptolite zone 13, the basal part of the Maravillas chert, is well devel­oped in the Snake Hill and Canajoharie shales, in the Nowadaga and Loyal Creek members of the Utica shale in New York, and in the Magog shale in Quebec. Also, the lower part of the Viola limestone and the upper part of the Womble shale have several species in common with graptolite zone 13. Further, the most characteristic form in zone 13, Orthograptus truncatus var. intermedius, was identified by the writer in Ruedemann's collections from the Trenton limestone from Trenton Falls near Middleville, New York. King ( 1937, p. 41) listed a few ostracods collected from rocks which are within zone 13. Ulrich worked on King's collection and identified six genera but was able to determine the species of only one of them. All of the genera are re­corded from the Bromide formation (Harris, 1939), but they all apparently have some range in time since all are also found in the Decorah formation (Kay, 1940). The Decorah has been put in the Trenton stage by Cooper ( 1956) . Graptolite zone 14, the middle part and some of the upper part of the Maravillas chert, the Bigfork chert, and the middle and upper parts of the Viola limestone have a few species in common, including Dicellograptus f orchammeri, Orthograptus truncatus var. recurrens, and Leptograptus annectans. In New York, the Holland Patent, Deer River, and Atwater Creek shales and the Lorraine group have a few species of graptolites in common. These species include Orthograptus quadri­mucronatus, Orthograptus truncatus var. recurrens, and Climacograptus typicalis. The species 0. quadrimucronatus, 0. truncatus var. recurrens, C. typicalis, and L. annectans are commoJl. to both the New York and Marathon successions, and zone 14 is considered correlative with the Holland Patent, Deer River, At­water Creek, and Lorraine formations in New York. The highest 50 feet of the Maravillas chert, zone 15, the Polk Creek shale in the Ouachita Mountains, and the Sylvan shale in the Arbuckle Mountains have nearly identical graptolite faunas. The species Dicellograptus complanatus, Diplograptus crassitestus, and Climacograptus mississip­piensis are particularly common in all three formations. INTERCONTINENTAL CORRELATION A complete sequence of graptolite zones for the Ordovician system has been deline­ated in the Marathon region, and the cor­relation of some other graptolite-bearing rocks in North America with that zonal sequence has been considered. Complete sequences of Ordovician graptolite zones have been recognized in two other areas in the world. The most famous of these was worked out in the British Isles by Elles and Wood (1901-1918). Elles (1925) set forth the important features of the British zones in a concise manner. The other complete se­quence is that in Victoria, Australia, where T. S. Hall, Harris, Keble, Thomas, and others have collected graptolites strati­graphically for over 100 years. Several zonal schemes have been proposed for parts of the Victorian succession (Hall, 1899b, and Harris and Keble, 1932), but Harris and Thomas ( l 938b) have published the most recent discussion of the Australian Grapwlite Faunas, Marathon Region zones, and their work embraces all of the each area follows from the correlation of Ordovician system. the graptolite zones. The Victorian and Table 3 shows an attempt at correlation Marathon sequences are quite similar between the Marathon, Victorian, and throughout, but the British sequence in the British graptolite zones for the Ordovi­Early and early Middle Ordovician is dis­cian system. The correlation of the stages similar. and series of the Ordovician system in The lowest beds in the Ordovician sys- Table 3. Correlation of Ordovician sequences in the United States (Marathon area), Australia (Vic­toria), and the British Isles based on graptolite zones. U:'\ITED STATES Zone AUSTRALIA Zone BRITISH ISLES Zone Richmond 15 Bolindian 25 Ash gill 15 14 Mays,·ille Eden 14 24 23 13 12 Trenton 13 Eastonian 22 Cara doc 11 Wilderness 12 21 10 Porterfield 11 Gisbornian 20 9 Ashby ~farmor 10 9­ Middle Ordovician 19 18 17 16 Llandeilo 8 Whiterock 8 Yapeenian Castlemainian 15 14 13 12 Llanvirn 7 11 6 7 10 Chewtonian 9 Canadian series 6 5 4 Bendigonian 8 7 6 5 4 Arenig 5 4 3 3 2 Lancefieldian 3 2 2 1 1 Tremadoc 1 Bureau of Ecorwmic Geology, The University of Texas tern in Victoria, the Lancefield series, have been subdivided into three zones. The low­est zone is marked by the appearance of Staurograptus with two provincial species of Dictyonema. The lowest zone in the Marathon succession is characterized by the genus Anisograptus, but the fauna includes Staurograptus, which is restricted to the lowest zone. Zone 2 in the Marathon succession and the second zone in the Lancefield series contain several identical species including Clonograptus rigidus, Tetragraptus decip­iens, Adelograptus hunnebergensis, A. vic­torUie, and A. simplex. These two zones are, therefore, considered correlatives. The third zone in the Marathon succes­sion and the third zone of the Lancefield series also contain many identical species. The most diagnostic species of both zones is Tetragraptus approximatus. Associated with it are Clonograptus rigidus, C. ftexilis, Tetragraptus quadribrachiatus, and Dicho­graptus octobrachiatus. The appearance of T. approximatus and its associates marks the beginning of rapid speciation within the genera Didymograp­tus and T etragraptus. This speciation reaches its full development in the overly­ing strata. The complex composed of spe­cies of these two genera has been sub­divided into three zones in the Marathon region and six zones in Victoria. The rocks which are included in these six zones in Australia are much thicker than the rocks which comprise the corresponding zones in the Marathon region. In the Victorian suc­cession, the complex of Tetragrapti and ex­tensiform Didymograpti is found in the Bendigo and most of the Chewton series. The complex has been divided as follows: Bendigo series: basal zone characterized by T. approximatus with T. fruticosus (four-branched); second zone denoted by T. fruticosus (four-branched) without either T. approximatus or T. fruticosus (three-branched); third zone marked by the appearance of T. fruticosus (three­branched) with T. fruticosus (four­branched) ; fourth zone typified by T. fruticosus (three-branched) without T. fruticosus (four-branched). Chewton series: lowest zone marked by the appearance of the dependent didymo­graptid D. protobifidus with T. fruticosus (three-branched); second zone character­ized by D. protobifidus with T. fruticosus (three-branched) being rare. The three zones in the Marathon region which encompass the complex of Tetra­grapti and extensiform Didymograpti have been delimited as follows: zone 4 is charac­terized by the appearance of T. fruticosus (four-branched) without either T. ap­proximatus or T. fruticosus (three­branched); zone 5 is marked by T. fruti­cosus (three-branched) appearing with T. fruticosus (four-branched) ; and zone 6 is marked by the appearance of D. proto­bifidus with both the three-and four­branched forms of T. fruticosus. Thus the same theme of appearance of T. fruticosus (four-branched), then T. fruticosus (three­branched), then D. protobifidus obtains in both the Victorian and Marathon se· quences. Zone 4 of the Marathon sequence is con­sidered correlative with the lower two zones of the Bendigo series. Although the lowest zone of the series includes T. approximatus, the presence of T. fruticosus (four­branched) with several other species of Tetragrapti and Didymograpti in the same zone in Victoria makes the correlation of this zone with Marathon zone 4 more plausible than correlating it with Marathon zone 3. Zone 5 of the Marathon sequence and the third zone of the Bendigo series are characterized by the same forms (the three-and four-branched forms of T. fruticosus together) and they contain many identical species. The correlation of the highest zone of the Bendigo series with the Marathon zonal scheme is difficult because the four-branched form of T. f~uticosus ranges into the zone with D. protobifidus in Marathon but does not range above the third zone of the Bendigo series in Victoria. The fourth and highest zone of the Bendigo series does have a number of species identi­cal to those found in both zones 5 and 6 in Grapwlite Faunas, Marathon Region the Marathon succession, and the writer arbitrarily correlates the lower part of it with Marathon zone 5 and the upper part with Marathon zone 6. The lowest zone of the Chewton series and Marathon zone 6 are marked by the appearance of D. proto­bifidus, and they contain several identical species. The second zone in the Chewton series, characterized by D. protobifidus with T. fruti-cosus (three·hranched) rare, is also correlated with zone 6. Thus Mara­thon zone 6 is believed to be equivalent to part of the highest zone of the Bendigo series and the lower two zones of the Chewton series. Zone 7 of the Marathon sequence is characterized by the dependent didymo­graptids D. artus and D. bifidus, which give an important tie with the British zones (seep. 43). The fauna of the high­est zone of the Chewton series is poorly known and may he the correlative of zone 7, since it lies above the zone with D. protobifidus and below the zone with Iso­graptus caduceus var. lunata in the Vic­torian succession. These two forms occur respectively below and above D. bifidus in the Marathon sequence. The Castlemaine series in Victoria has been divided into three zones based on the appearance in succession of varieties of lsograptus caduceus. The succession is, in order of appearance, /. caduceus var. lunata, I. caduceus var. vicwriae, and /. caduceus var. maxima. The succeeding series, the Y apeen, has been divided into two zones, the lower of which is the zone of Oncograptus and the upper is the zone of Cardiograptus. I. caduceus var. lunata appears first in the Marathon region, but the other varieties of /. caduceus and the genera Oncograptus and Cardiograptus occur together; and, in fact, /. caduceus var. victoriae, Oncograptus upsilon, and Cardiograptus morsus have been found together on the same bedding plane. Further, Trigonograptus ensiformis and Didymograptus v-defl.exus occur with Oncograptus and Cardiograptus in both the Victorian and Marathon sequences. Thus zone 8 in the Marathon region, which includes Oncograptus, Cardiograptus, and the several varieties of/. caduceus, is cor­related with both the Castlemaine and Yapeen series in Victoria. The Middle Ordovician, as recognized in Victoria, includes four zones, while rocks containing the same species in the Mara­thon region have been found divisible into only two zones. All of the important species of the lower two zones and the lower part of the third zone of the Middle Ordovician of Victoria were found in zone 9 in the Marathon sequence. Harris ( 1935) listed the characteristic assemblages of grapto­lites in each zone of the Victorian Middle Ordovician, and by comparing these lists to the list of the fauna from zone 9, it will be noted that Glyptograptus austrodentatus and/. caduceus var. divergens, character­istic of the lowest zone of the Victorian Middle Ordovician; Glyptograptus inter­situs, Hallograptus etheridgei, Cryptograp­tus schaf eri, and Glossograptus acanthus, characteristic of the second zone of the Victorian Middle Ordovician; and Didy­mograptus nodosus, H allograptus etherid­gei, and Didymograptus cuspidatus, char­acteristic of the lower part of the third zone of the Victorian Middle Ordovician, are all found in zone 9. The diagnostic species in the upper part of the third zone of the Victorian Middle Ordovician (Am­plexograptus confertus, A. difjertus, and Phyllograptus nobilis) and diagnostic species of the fourth and highest zone of the Victorian Middle Ordovician ( Glypto­gmptus teretiusculus and Climacograptus riddellensis) comprise the fauna of zone 10 in the Marathon sequence. The fauna of the Upper Ordovician in Victoria has not been worked out in detail stratigraphically, nor fully described. Thomas and Kehle (1933) published lists of graptolites collected from various Upper Ordovician localities, hut only recently (Harris and Thomas, 1955) has any sys­ tematic paleontology been done on the Late Ordovician faunas. Harris and Thomas ( 1938h) gave a brief list of the diagnostic species of each zone. Three series were dis­ tinguished in the Victorian Upper Ordo­ Bureau of Economic Geology, The University of Texas v1c1an. In ascending order they are Gis· bornian, Eastonian, and Bolindian. Two zones were recognized in the Gisbornian series; the lower is the zone of Nema· graptus gracilis and the upper is the zone of Climacograptus peltifer. Zones 11 (zone of N. gracilis) and 12 (zone of Climaco­graptus bicornis) in the Marathon sequence contain many of the same species as are re· ported in the two zones in the Gisbornian. Two zones were also recognized in the Eastonian series. The lower zone includes the species Dicranograptus nicholsoni and Orthograptus truncatus, both of which are common in zone 13 of the Marathon se· quence. Zone 14 in the Marathon region includes elements of both the upper zone of the Eastonian series (Climacograptus tubulif er us, C. minimus, Orthograptus cal­caratus var. vulgatus) and of the lower zone of the Bolindian series (Orthograptus quadrimucronatus and Dicellograptus for­chammeri). The highest zone of the Mara· thon sequence, zone 15, and the highest zone of the Bolindian series are character· ized by DiceUagraptus complanatus and D. complanatus var. ornatus. Thus the Victorian and Marathon zonal sequences are quite similar for all of Ordo­vician time. However, the lower and middle parts of the British sequence are rather dis­similar to the lower and middle parts of the Marathon and Victorian sequences, and correlation between the areas is far more difficult. The lower zone of the Tremadoc series, the lowest zone in the British succession, is denoted by varieties of the species Dictyonema fiabellif or me, but these forms do not occur in either North America or Australia. However, Bulman (1954) in a study of the Dictyonema shales (lower Tremadoc) of the Oslo region, Norway, pointed out the possibility that the Matane shale in Quebec, which is a correlative of the lowest zone in the Marathon sequence, may be lower Tremadoc in age. The genus Anisograptus, which is diagnostic of zone 1 in the Marathon region, was found in the Oslo region with the varieties of Dictyo· nema fiabelliforme which characterize the lower Tremadoc. The lowest zones of the Victorian and Marathon areas are correla­tives, and both are probable correlatives of the lower zone in the Tremadoc series in the British Isles. The rocks comprising the upper part of the Tremadoc series and the basal part of the Arenig series do not contain graptolites in the type localities of these series. How· ever, Elles (in Elles and Wood, 1901­1918) suggested a second zone at the top of the Tremadoc and a third zone at the base of the Arenig. As recognized by Elles, the second zone of the British sequence is characterized by the appearance of Cl.onograptus and species now placed in the genus Adelograptus. These two genera are diagnostic of the second zone of both the Victorian and Marathon sequences. Although the genera are the same in both the British and Mara· thon· Victorian sequences, only one species, Clonograptus tenellus var. callavei, is found to be common to the British and the Mara­thon zonal assemblages. The writer con­siders the second zone in all three se· quences to be correlative. According to Elles (1922) , the third British zone, the lowest of the Arenig se· ries, is characterized by the multiramous dichograptids Clonograptus fiexilis and Dichograptus octobrachiatus in the lower part and by the incursion of tetragraptids in the upper part. However, recent work has led Bulman ( 1958, p. 164) to state that there is no stratigraphic evidence for the existence of this zone. The complex of tetragraptids and ex· tensiform didymograptids, so characteristic of zones 4, 5, and 6 in the Marathon region and of the Bendigo and part of the Chew· ton series in Victoria, is also found in the British Isles. It has been divided into two main zones (zones of Didymograptus ex· tensus and D. hirundo) (Elles and Wood, 1901-1918) , and Elles (1933) subdivided the D. extensus zone into four subzones. Detailed correlation between the subzones and the Marathon and Victorian zones is tenuous, however. Didymograptus proto­bifidus appears first in the British succes­ Graptolite Faunas, Marathon Regi,on sion in the third subzone, that of Didymo­graptus nitidus, and it appears in zone 6 of the Marathon sequence and in the lowest zone of the Chewton series in Victoria. The presence of this early dependent didymo­graptid indicates the possibility that the lower two subzones of the D. extensus zone may be correlative with the Bendigo series in Victoria and with zones 4 and 5 in the Marathon region. Zone 6 in Marathon and the lower two zones of the Chewton series in Victoria both are typified by D. proto· bifidus and include D. protobifidus-D. bifidus transients. The third subzone of the D. extensus zone contains D. protobifidus, and the highest subzone and the succeeding zone, that of D. hirundo, both have D. pro­tobifidus-D. bifidus transients. Thus zone 6 in the Marathon region, the lowest two zones of the Chewton series, and the upper two subzones of the D. extensus zone plus the D. hirundo zone are probable correla­tives. The two species which are diagnostic of zone 7 in the Marathon sequence, Didymo· graptus artus and D. bifidus, are also the diagnostic species of the sixth zone, the basal zone of the Llanvirn series, in the British Isles. The occurrence of these two important species as zonal indicators in both the British and Marathon successions affords a good tie point between these two otherwise dissimilar zonal subdivisions of the lower and middle parts of the Ordo­vician system. The highest zone of the Chewton series is correlated with zone 7 in the Marathon region and is thus a probable correlative of the sixth zone in the British Isles. The highest subzone of the D. extensus zone of the British succession includes lso­graptu,s, Oncograptus (Cummins, 1954), Glypt-0graptus dentatus, and Trigonograp· !us ensifonnis with the complex of tetra· graptids and extensiform didymograptids and the D. prowbifidus-D. bifidus tran­sients. The writer considers the appearance of the dependent didymograptids with the extensiform types and with the tetragrap­tids and the subsequent appearance of D. bifidus and D. artus to be more important for correlation than the presence of lso­graptus, Oncograptus, Glyptograptus, etc., which appear in zone 8 in the Marathon region and in the Castlemaine and Y apeen series in Australia. Contrary to the opinion of others (Ripper, 1937; Harris and Thomas, 1938b), the writer believes that the lsograptus, Oncograptus, and biserial scandent forms appear in older beds in the British sequence than they do in the Vic· torian and Marathon. These forms are less common in the British sequence than they are in either the Marathon or Victorian and appeared in Britian first, then in North America and Australia. The seventh zone of the British sequence, the upper of the Llanvirn series, has few elements in common with the Marathon and Victorian successions. However, the eighth zone, that of the Llandeilo series, is characterized by the presence of Glypto· graptus teretiusculus in abundance, and the same criterion is used to delimit zone 10 of the Marathon sequence and the upper· most zone of the Middle Ordovician in Vic­toria. Zone 7, the upper zone of the Lian· vim series, is correlated with zones 8 and 9 in the Marathon sequence and with the Castlemaine and Y apeen series and the lower three zones of the Middle Ordovician in Victoria because of its stratigraphic position. With the incursion of G. teretiusculus in abundance in all three zonal successions, similar assemblages appear in the same se· quence in all three areas during the re­mainder of Ordovician time. Harris and Thomas ( l 938b) used the same zone names as the British (with the exception of that of Dicellograptus anceps, the fauna of which, they stated, is included in the zone of Dicellograptus complanatus), and they indicated that the fauna of each zone is quite similar to that of the British zones. N emagraptus gracilis and its associates mark zone 11 in the Marathon region, the basal zone of the Gisbornian series in Aus­tralia, and the basal zone of the Caradoc series in the British Isles. Zone 12 in the Marathon region, the upper zone of the Gisbornian series in Victoria, and the tenth Bureau of Economic Geology, The University of Texas zone in the British succession have many species in common and are characterized by the incursion of large Orthograpti, the presence of Climacograptus bicomis and its variety peltifer, and the absence of the Nemagrapti. The appearance of several species of large orthograptids marks zone 13 in the Marathon region, the lower zone of the Eastonian series in Victoria, and the eleventh zone of the British sequence. The form Orthograptus truncatus var. inter­medius is common in both Marathon zone 13 and the eleventh British zone. Zone 14 in the Marathon succession contains ele­ments of both zones 12 (zone of Dicrano­graptus clingani) and 13 (zone of Pleuro­graptus linearis) of the British sequence and is probably correlative with both, but no subdivision is feasible in the Marathon region. The species Orthograptus truncatus and Orthograptus calcaratus, which occur in zone 14, are diagnostic of the zone of D. clingani, and Orthograptus quadrimu­cronatus, which is common in zone 14, is diagnostic of the zone of Pleurograptus linearis in the British Isles. The upper zone of the Eastonian series in Victoria contains the same characteristic species as zone 12 (the zone of D. clingani) in the British Isles, and the lower zone of the Bolindian series has 0. quadrimucronatus and P. line­aris, which are distinctive of zone 13 in the British Isles. The forms Dicellograptus complanatus and D. complanatus var. ornatus are char­acteristic of the uppermost zone of the Marathon sequence, zone 15, and are found in the upper zone of the Bolindian series in Australia. In the British Isles, D. com­planatus is the diagnostic element of zone 14, the lower zone of the Ashgill series, and the variety ornatus occurs with D. anceps in zone 15. Elles (1937, pp. 488-489) stated that the zone of D. complanatus is conditional and omitted it from her charts of the zones. Zone 15 of the Marathon se­quence includes species (Orthograptus truncatus var. abbreviatus? and Dicello­graptus complanatus var. ornatus, etc.) found in the D. anceps zone in the British Isles, and hence it is correlated with the Ashgill series there. Thus the Marathon and Victorian zonal sequences are quite similar throughout but are dissimilar to the British sequence until the Llandeilo. From then on, the zonal as­semblages in all three areas are similar. North America and Australia belonged to one graptolite faunal region and the British Isles were a part of another during pre· Llandeilo time. From that time throughont the remainder of the Ordovician, graptolite species occurred in similar assemblages in the same sequence in all three areas. SYSTEMATIC PALEONTOLOGY The writer has followed Bulman's ( 1955) taxonomic subdivisions as pub­lished in the section on Graptolithina in the Treatise on Invertebrate Paleontology. Reference is made to the Elles and Wood ( 1901-1918) and Ruedemann (1904, 1908, and 1947) monographic works on the Graptolithina and to the more readily accessible Australian publications for de­tailed descriptions of the species and sub­species. Differences between the Texas specimens and the published descriptions are noted, and the geographic and geologic range of each species and subspecies is given. Class GRAPTOLITHINA Bronn, 1846 Order DENDROIDEA Nicholson, 1872 Family DENDROGRAPTIDAE Roemer (in Frech, 1897) Genus DICTYONEMA Hall, 1851 DICTYONEMA DUMOSUS Berry, n. sp. Pl. 7, fig. 10 Descriptwn.-Therhabdosome is broadly conical and medium-sized, measuring 1.7 cm in length and 2.5 cm in width. The stipes are wavy, are 0.2 to 0.3 mm in width, number 15 to 16 in 10 mm in the mature portion of the rhabdosome, and di­vide frequently at first but subsequent di­visions are spaced farther and farther apart. The stipes divide at acute angles (20 to 30 degrees) but become sub­parallel immediately. The space between the stipes is 1 mm in the mature portion of the rhabdosome. Dissepiments are infre­quent and are as thick as the stipes. The dis­sepiments usually occur between stipes when the bulge or wave in one stipe nearly touches a similar bulge in the stipe next to it. The thecae are indistinct but the auto­thecae appear to number 14 to 16 in 10 mm, and in flattened profile view may be seen alternating on both sides of the stipes, giving them wrinkled outer edges. Horizon.-The specimens of this species were collected from one locality (collection 101) which is in zone 4 in the upper part of the Marathon limestone. Holotype.-Yale Peabody Museum No. 20251. Family ANISOGRAPTIDAE Bulman, 1950 Genus ANISOGRAPTUS Ruedemann, 1937 ANISOGRAPTUS DISSOLUTUS Berry, n. sp. Pl. 4, figs. 5, 6 Description.-The rhabdosome is tri­radiate and horizontal, with somewhat flowing branches which bifurcate at in­creasing intervals. The three first-order branches are 2.0 to 2.8 mm in length, and commonly one is longer than the other two. Bifurcations occur at intervals of 2.0 to 2.8 mm, 3.0 to 4.0 mm, and 4.5 to 5 mm up to the fourth order, above which, branching is irregular and does not occur in some stipes. The first-order stipes are 0.3 mm wide, while the fifth and sixth order stipes are 0.6 to 0.7 mm in width. The thecae number 11 to 12 in 10 mm. The autothecae have a nearly straight ventral margin, a slightly concave apertural margin, and overlap about one-half their length. This species resembles A. fiexuosus in its lax shape and the tangle formed by the distal branches. It differs from that form in the branching, the number of thecae per 10 mm, and the lack of denticles on the autothecae. Horizon.-Specimens of this species were collected from the lower part of the Marathon limestone, zone 1 (collection 84A). Holotype.-Yale Peabody Museum No. 20255. Genus ADELOGRAPTUS Bulman, 1941 ADELOGRAPTUS HUNNEBERGENSIS (Moberg)? Pl. 5, figs. 2, 8 Remarks.-The Texas specimens are poorly µreserved and are small. However, they agree with the specific description given by Moberg (1892) and the more complete discussion by Stubblefield ( 1929) in the following characteristics: the length Bureau of Economic Geology, The University of Texas of the sicula (1.0 mm), the angle of the divergence of the primary stipes (130 to 140 degrees), the dichotomy just past the opening of the third theca, the number of the thecae per 10 mm (8 to 9 in 10 mm), and the concave apertural margins of the thecae. The thecal overlap of the Texas specimens is about one-third their length, while in the type material the thecae over­lap one-half their length. Also, the primary stipes in the Texas specimens are 0.5 to 0.7 mm in width, while the same stipes are 0.8 mm in width in Stubblefield's picture. Be­cause of the smaller size and the poor pre­servation of the Texas material, they are only tentatively referred to A. hunneberg­ensis. Horizon.-The specimens provisionally referred to this species were collected from low in zone 2 (collections 11 and 59) in the lower part of the Marathon limestone. Stubblefield records A. hunnebergensis from the Shineton shales (Tremadoc in age) in Shropshire. Moberg originally' de­scribed the species from rocks of Tremadoc age in Sweden. ADELOGRAPTUS PUSILLUS (Ruedemann) Bryograptus pusillus Ruedemann, 1904, N. Y. State Mus., Mem. 7, pp. 641, 642, pl. 4, figs. 21, 22. Bryograptus pusillus Ruedemann, 1947, Geo!. Soc. America Mem. 19, p. 299, pl. 49, figs. 3, 4 (not figs. 5, 6). Remarks. -Bulman (1941) removed pendent multiramous dichograptids with two primary stipes from the genus Bryo­graptus and placed them in the genus Adelograptus. Two primary stipes origi­nate from the sicula in the species pusillus and hence it belongs in the genus Adelo­graptus. The Texas specimens agree closely with Ruedemann's original specific descrip­tion. The forms from the Glenogle shale figured by Ruedemann ( 1947) as Bryo­graptus pusillus (Pl. 49, figs. 5, 6) appear to the writer to belong to the genus Ptero­graptus. Horizon.-A. pusillus was obtained from zone 4 in the upper part of the Marathon limestone (collection 71). Ruedemann (1947) reports the species from bed 2 of the T etragraptus zone of the Deepkill shale in New York. ADELOGRAPTUS SIMPLEX (Tornquist) Bryograptus simplex Tornquist, 1904, Lunds Univ. Arsskrift, Bd. 40, Afdeln 1, no. 2, pp. 3-4, p I. 1, figs. 1-4. Bryograptus simplex Benson and Keble, 1935, Royal Soc. New Zealand, Trans., vol. 65, p. 270, pl. 30, figs. 12, 13. Adelograptus simplex Bulman, 1941, Ann. Mag. Nat. Hist., ser. 11, vol. 7, p. 115. Remarks.-The Texas specimens agree in all essential characters with Tornquist's description except that the inclination of the thecae is slightly less than in the type material and as a consequence, the stipes are not quite so wide. Many of the Texas forms are immature. Horizon.-Specimens of this species were collected from the lower part of the Marathon limestone, zone 2 (collections 33, 37, and 72E). Tornquist's type material came from the lower Phyllograptus shales (zone of T etragraptus phyllograptoides) in Sweden. Benson and Keble (1935) state that in New Zealand, the species occurs oc­casionally in the lowest zone of the Bendigo series but is more common in the zones be­low, the upper two zones of the Lancefield series. Harris and Thomas ( 1938b) figure A. simplex as common in the second zone of the Lancefield series of Victoria, Aus­tralia. The species occurs with the same associates (A. victoriae, Tetragraptus de­cipiens, and Clonograptus fiexilis) in the Lancefield series and zone 2 in the Mara­thon sequence. ADELOGRAPTUS VICTORIAE (T. S. Hall) Bryograptus victoriae T. S. Hall, 1898, Royal Soc. Victoria, Proc., vol. 11, p. 165, pl. 17, figs. 1, 2. Adelograptus victoriae Bulman, 1941, Ann. Mag. Nat. Hist., ser. 11, vol. 7, p. 115. Remarks.-The Texas specimens agree closely with Hall's specific description. Horizon.-Specimens of A. victoriae were collected from the lower part of the Marathon limestone (collections 33, 43, 72E, 7 4, and 89), where it is a charac­teristic element of the fauna of zone 2. Harris and Keble ( 1932) list the species as a common form of the second zone in the Grapwlite Faunas, Marathon Region Lancefield series of the Lower Ordovician of Victoria, Australia. A. vicwrUie occurs with the same associates (Clonograptus rigUlus, Adelograptus simplex, and Tetra­graptus decipiens) in both the Victorian and Marathon sequences. Genus BRYOGRAPTUS Lap,.·orth, 1880 BRYOGRAPTUS CRASSUS Barris and Thomas? Pl. 5, fig. 9 Remarks.-The Texas specimens are poorly preserved but three primary stipes appear to be present, thus indicating the generic affinities are with Bryograptus rather than Adelograptu.s. No more than four secondary stipes were seen in any of the Texas material, while Harris and Thomas (1938a, pp. 72-73, pl. 1, figs. 7a-d, pl. 4, fig. 6) figure forms with four to six secondary stipes. Harris and Thomas mention two primary stipes only, but three primary stipes appear to be present in the Texas specimens. However, the Texas spe· cimens agree with Harris and Thomas' specific description in the width of the stipes, in the angle of divergence of the stipes, and in the manner in which the stipes branch. Horizon.-The specimens tentatively re­ferred to B. crassus were collected from the lower part of the Marathon limestone, zone 2 (collections 33 and 3 7) . The type specimens of B. crassus came from the basal zone of the Bendigo series in Vic­toria, Australia; the Texas forms occur at a lower horizon than do the Australian. Genus CLONOGRAPTUS Ball and Nicholson, 1873 CLONOGRAPTUS FLEXILIS (Ball) Pl. 6, fig. 4 Graptolithus f/exilis Hall, 1858, Geo!. Survey Canada, Rept. Prog:. for 1857, pp. 119, 145. Clonograptus f/exilis T. S. Hall, 1899, Royal Soc. Victoria, Proc. ( n.s.), vol. 11, p. 169, pl. 19, fig. 20. Clonograptus f/exilis Ruedemann, 1947, Geo!. Soc. America Mem. 19, pp. 280-281, pl. 44, figs. 4--9. Remarks.-The measurements of the Texas specimens agree with those given by Ruedemann, except that the funicle length of the Texas forms is slightly less (2.0 mm compared to 2.5 mm in the type ma­terial). Horizon.-Specimens of C. flexilis were collected from zones 2, 3, and 4 in the lower and middle parts of the Marathon limestone (collections 2, 11, 33, 69, 76, and 97B). The species was described by J. Hall from the Levis shale in Quebec, and Ray­mond (1914) found it there in association with C. rigUlus and Tetragraptus approxi­matus and placed the assemblage in his lowest zone, zone A. This assemblage is identical to that of zone 3 in the Marathon succession. Harris and Thomas (1938b) record C. fl.exilis from the lower two zones of the Lancefield series in Victoria, Aus­tralia, where it occurs with the same as­sociates as it does in zones 2 and 3 of the Marathon sequence. CLONOGRAPTUS PERSISTENS Harris and Thomas Pl. 5, fig. 11 Clonograptus persistens Harris and Thomas, 1939, Min. and Geol. Jour., vol. 2, p. 59, fig. 11. Original diagnosis. -Rhabdosome of typical clonograptid aspect, up to 14 cm in diameter, the longest stipes measured, usually those produced by the last dichot­omy, being 3.5 cm long. Funicle 4 mm in length. Stipes up to the fifth or seventh order are found, all the stipes being of approximately the same width-about 1.5 mm. Thecae 9 to 10 in 10 mm, inclined at 25 to 45 degrees, with convex ventral mar­gins, overlapping for half their length. Remarks.-The Texas specimens agree with the above description except that the fourth order stipes are slightly longer than those shown in the figure of the Australian specimen. Horizon.-C. persistens was found to be a common element of zone 2, in the lower part of the Marathon limestone (collections 12 and 33) . Harris and Thomas state that their type specimen came from the lowest zone of the Bendigo series in Victoria, Australia. The species occurs there at a slightly younger horizon than it does in the Marathon region. Bureau of Economic Geology, The University of Texas CLONOGRAPTUS RJGIDUS (Hall) Pl. 5, fig. 10; Pl. 7, fig. 15 Graptolithus rigidus Hall, 1858, Canadian Nat. Geo!., vol. 3, p. 146. Clonograptus rigidus T. S. Hall, 1899, Royal Soc. Victoria, Proc. (n.s.), vol. 11, p. 170, pl. 18, fig. 22, pl. 19, fig. 21. Clonograptus rigidus Ruedemann, 1947, Geo!. Soc. America Mem. 19, pp. 281-282, pl. 44, figs. 10, 11. Remarks.-The Texas specimens agree well with the description by Ruedemann. The stipes are rigid and definitely thicker than those of C. fiexilis, which is quite like C. rigidus in other respects. In C. rigidus the funicle and second order stipes measure 1 to 2 mm in width, whereas in C. fiexilis the same stipes measure but 0.4 mm in width. Horizon.-C. rigidus was collected from zones 2 and 3, the lower and middle parts of the Marathon limestone (collections 11, 76, and 84). Raymond (1914) records the species from zone A of the Levis shale with C. fiexilis and T. approximatus (an identi­cal assemblage to that of zone 3 of the Marathon sequence). Harris and Thomas (l938b) report the species from the upper two zones of the Lancefield series in Vic­toria, Australia, with the same associates as in North America. CLONOGRAPTUS el. C. TENELLUS (Llnnanon) Pl. 4, figs. 1-3 Remarks.-The Texas specimens re­semble C. tenellus in the extreme tenuity of the stipes and in general shape of the rhabdosome. However, the funicle lenoth (1.5 mm) is less than that of Linnarso~'s types (Linnarson, 1871, Ofv. Kong!. Vet. Akad. Forh. Stockholm, vol. 28, p. 795, taf. 16, figs. 13-15). Also, the second order stipes are 2.0 to 2.2 mm in length whereas the same stipes of the type material are 3.8 to 4.0 mm in length. Only a few thecae of the Texas specimens are well preserved and they number 8 to 9 in 10 mm whereas those of the type number 9 to 10 in 10 mm. In shape of the thecae, the Texas specimens agree with the description of the type ma· terial. They are slender tubes, widening slightly toward their apertures, are in-dined at 20 degrees to the stipe, and over­lap for a small portion of their length. Horizon.-The specimens tentatively re· £erred to this species were collected from the lowest beds of the Marathon limestone, zone 1 (collections 72B and 119), where they are associated with anisograptids. Elles and Wood report the species C. tenel­lus is in the Tremadoc beds and the lower part of the Skiddaw slates in the British Isles. CLO:\"OGRAPTUS TENELLUS var. CALLAVEI (Lapworth) ?Bryograptus callavei l..apworth, 1880, Ann. Mag. Nat. Hist., vol. 5, p. 165, pl. 5, fig. 21. Clonograptus tenellus var. callavei Elles and Wood, 1902, Mon. British Grapt., p. 84, pl. 11, figs. 3a-c. Remarks.-The Texas specimens have a well-developed web structure around the first and second order stipes, otherwise they agree with Elles and Wood's descrip­tion. The variety is characterized by its short, wide stipes, which are much wider than in the typical C. tenellus. Horizon.-A few specimens of this va­riety were collected from low in zone 2 (collection 84) , in the lower part of the Marathon limestone. Elles and Wood re­cord this variety from the Tremadoc, Shineton shales. Genos TRIOGRAPTUS Monsen, 1925 TRIOGRAPTUS cl. T. OTAGOENSIS Benson and Keble Pl. 4, fig. 7 Remarks.-The Texas specimens are poorly preserved and the details of the thecae cannot be clearly seen. However, the specimens agree with the description of T. otagoensis by Benson and Keble ( 1935, pp. 279-280, pl. 31, figs. 11-13) in having three straight stipes which enclose an angle of about 120 degrees and which rapidly at­tain a width of 0.5 to 0.7 mm and then maintain that width. Also, the thecae over­lap about one-half their length and are in­clined at a low angle (10 to 15 degrees) to the stipe. Further thecal details are oh· scure in the Texas specimens. In none of them do the stipes measure more than 5 mm, whereas Benson and Keble state that Graptolite Faunas, Marathon Region in some of their forms the stipes attain a length of 20 mm. Although the Texas speci­mens are like T. otagoensis in gross aspect, they are referred to that species only tenta­tively because many details are obscured by the poor preservation. Horizon.-The specimens referred to T. otagoensis were collected from the lower part of the Marathon limestone, zones 1 (collection 29) and 2 (collections 72D and 84) . Benson and Keble record the species from New Zealand with an assem­blage that is similar to that of zone 2 in the Marathon limestone. Family PTILOGRAPTIDAE Hopkinson, 1875 Genus PTILOGRAPTUS Hall, 1865 PTILOGRAPTUS PLUMOSUS Hall Pl. 7, fig. 6 Ptilograptus plumosus Hall, 1865, Canadian Or­ganic Remains, p. 140, pl 21, figs. 1-4. Ptilograptus plumosus Ruedemann, 1947, Geol Soc. America Mem. 19, p. 247, pl 33, figs. 1-8. Remarks.-The Texas specimens agree well with the specific description by Rue­ demann. Horizon.-Specimens of P. plumosus were collected from zone 4 of the upper part of the Marathon limestone (collection 121) and zone 9, the upper part of the Fort Pena formation (collection 28). Hall's types came from the Levis shale at Point Levis, Quebec, and Raymond (1914) lists it in his zone C-1, the lowest DU!ymo­graptus zone of the Levis shale. Ruede­mann records the species from graptolite bed 7, zone of Dipwgraptus dentatus, of the Deepkill shale in New York. The spe­cies appears to have as long a range in eastern North America as it does in the Marathon region. Order GRAPTOLOIDEA Lapworth, 1875 Family DICHOGRAPTIDAE Lapworth, 1873 Section GONIOGRAPTI Genus GONIOGRAPTUS MeCoy, 1876 GONIOGRAPTUS PERFLEXILIS Ruedemann Goniograptus perflexilis Ruedemann, 1904, New York State Mus. Mem. 7, pp. 625-627, text figs. 39a-d, pl. 6, figs. 16-18, pl 7, figs. 1-4, 6-9. Goniograptus perfiexilis Ruedemann, 1947, Geol Soc. America Mem. 19, p. 297, pl. 48, figs. 10-15. Remarks.-The Texas specimens agree well with Ruedemann's specific descrip­tion. Horizon.-A few specimens of G. per­fiexilis were collected from one locality (collection 4 7) which is in the highest beds of the Marathon limestone, zone 7. Ruede­mann records the species as common in the upper part of the Tetragraptus horizon (graptolite zone 1) and as rare in the next higher horizon (zone of DU!ymograptus bifidus) of the Deepkill shale in New York. Raymond (1914) lists it from zones C-3 and D (zones of D. bifidus and Diplo­graptus dentatus) of the Levis shale in Quebec. GONIOGRAPTUS THUREAUI (McCoy) Pl. 8, fig. 15 Didymograptus (Goniograptus) thureaui McCoy, 1876, Ann. Mag. Nat. Hist., ser. 4, vol 18, pp. 128---130. Goniograptus thureaui Ruedemann, 1904, New York State Mus. Mem. 7, pp. 621--024, text figs. 37, 38, pl 6, figs. 1-15. Goniograptus thureaui var. postremus Ruede­mann, 1947, Geol Soc. America Mem. 19, pp. 295-296, pl. 48, figs. 2-9. Remarks.-The Texas specimens agree fully with McCoy's specific description. The maximum number of stipes observed was 24, but some of the Australian forms have as many as 40. Ruedemann (1947) gave the varietal name postremus to forms with few stipes; however, McCoy's descrip­tion does not set a limit on the number of stipes a form must have to be included in the species G. thureaui, and the Australian workers include forms with a few as well as many stipes in this species. Therefore, the writer includes Ruedemann's variety postremus with the typical form of the species. Horizon.-A few specimens of G. thureaui were collected from one locality (collection 25) which is in the upper part of the Marathon limestone, zone 6. McCoy's types came from the Bendigo series in Vic­toria, Australia. Harris and Keble ( 1932) record the species as common in the zones of Tetragraptus fruticosus (three-branched form) and T. fruticosus (four-branched form) with T. fruticosus (three-branched Bureau of Economic Geology, The Univer&ity of Texas form), which are the middle part of the Bendigo series. Ruedemann states that his Yariety postremus is common in graptolite bed 2 ( T etragraptus zone) and that it ex­tends into the next zone ( Didymograptus bifidus zone) of the Deepkill shale in l\ew York. Ruedemann also records it from the Le\·is shale in Quebec. Genus BRACHIOCRAYITS Harris and Keble, 1932 BRACHJOCRAP'ITS ITAFOR"'IS Harris and Keble Brach;o!!raptus eta/ormis Harris and Keble, 1932, Royal Soc. Yictoria, Proc. ( n.s.), rnl. 44, p. 44. pl. 6, fig5. 8, 9. Remarks.-The Texas specimens agree well with the specific description by Harris and Keble. Two forms figured by Ruede­mann (19-17, pl. 45, figs. 15, 16) as Lo­ganograptus logani mut. pertenuis should be referred to B. etaformis. Hori;on.-A few specimens of B. eta­formis were collected from one locality (collection 28 ) which is in the upper part of the Fort Pena formation, zone 9. Harris and Keble list the species from the middle part of the ~fiddle Ordovician (zonf' of Diplograptus decoratus) in Victoria, Aus­tralia. Its associates in both the Victorian and ~Iarathon successions include Did'ymo­graptus nodosus, Trigonograptus ensi­formis, and Cr,-ptograptus schaferi. Genus LOCA_"\OCRAP'I1JS Hall, 1868 LOCA.."\OCRA.PTI.."S LOCA_"\I (Hall) Graptolithus logani Hall, 1858, Geo!. SurYey of Canada. Rept. Prog. for 1857, p. 115. Loganograptus logani Elles and Wood, 1902, :'\Ion. Briti>h Grap! .. pp. 81-82, pl. 11, figs. la-g. Loganograptus lo.eani Ruedemann. 1947. Geo!. Soc. America :\fem. 19, pp. 286-287, pl. 45, figs. 11-13. pl. 46, fig5. l, 2. Remarks.-The Texas specimens agree with the description by Ruedemann ex­cept that the width of the first and second order stipes is 0.6 to 0.7 mm. whereas Ruedemann giws a width of 0.8 mm for the same stipes. The fourth order stipes widen from 0.7 mm at their origin to a maximum of 1.6 mm distally. The second order stipes of the Texas specimens are 1.3 to 1.4 mm in length. and in his description, Ruedemann states that the second order stipes "are about 1.4 mm long." Horizon.-Ruedemann (in Sellards, 1933) first reported l. logani from the Marathon region. The writer collected it from the upper part of the Fort Pena for­mation, zone 9 (collections 13 and 28). Ruedemann records the species from grap­tolite bed 7 (zone of Diplograptus den­tatus) of the Deepkill shale in New York, and Raymond (1914) lists it from his zone D-2 (zone of D. dentatus) of the Levis shale in Quebec. Elles and Wood describe l. logani from the Arenig, middle part of the Skiddaw slates in the British Isles. Harris and Keble 11932) list it among the characteristic forms of the highest zone (zone of lsograptus caduceus var. maxi­ma) of the Castlemaine series in Victoria, Australia, and Harris (1935) lists it as very rare in the zone of Glyptograptus in­tersitus in the Middle Ordovician of the Victorian sequence. LOCA_"\OGRA.PTUS LOGA_"\1 mat• .PERTENUIS Ru.edemann Pl. 12, fig. 5 Lo,ganograptus lo,gani mut. pertenuis Ruedemann, 1904, New York State Mus. ~fem. 7, p. 633, pl. 9, fig. 5. Loganograptus logani mut. pertenuis Reudemann, 19-li. Geo!. Soc. America Mem. 19, p. 287, pl. 45, fig. 14 (not figs. 15, 16). Remarks.-The Texas specimens agree well with Ruedemann's description. This variety is like the typical form of l. logani except that it is much thinner (0.2 to 0.3 mm in width compared to 0.7 to 0.8 mm in width). Also, the thecae number 10 to 12 in 10 mm in this variety while they number 8 to 10 in 10 mm in the typical form. Two forms figured by Ruedemann (1947, pl. 45, figs. 15, 16) do not belong to this variety but should be referred to Brachiograptus etaformis. Horizon.-A few specimens of this thin variety of l. logani were collected from one locality (collection 28) which is in the upper part of the Fort Pena formation, zone 9. Ruedemann reports the variety to be rare in graptolite bed 7 of the Deepkill shale in New York. Graptolite Faunas, Marathon Region Genus PTEROGRAPTUS Holm, 1881 PTEROGRAPTUS INCERTUS Harris and Thomas Pl. 12, fig. 2 Pterograptus incertus Harris and Thomas, 1935, Royal Soc. Victoria, Proc. (n.s.), vol. 47, pp. 289-290, fig. 1, nos. 1, la, fig. 2, nos. 1-6. Remarks.-The Texas specimens agree well with the specific description by Harris and Thomas. Many of them are immature forms. Horizon.-P. incertus was collected from the upper part of the Fort Peiia formation, zone 9 (collections 16, 28, and 152). Harris and Thomas record it from the lower two zones (zones of Glyptograptus austroden­tatus and G. intersitus) of the Middle Ordo­vician in Victoria, Australia. The species occurs with many of the same associates (G. intersitus, Trigonograptus ensiformis, and Cryptograptus schaferi) in both the Marathon and Victorian sequences. Genus TRICHOGRAPTUS Nicholson, 1876 TRICHOGRAPTUS IMMOTUS Harris and Thomas Trichograptus immotus Harris and Thomas, 1935, Royal Soc. Victoria, Proc. (n.s.), vol. 47, pp. 290-291, fig. 1, nos. 2a-c, fig. 2, nos. 7, 8. Remarks.-The Texas specimens agree well with the specific description by Harris and Thomas. Horizon.-A few specimens of this spe­cies were collected from the upper part of the Fort Peiia formation, zone 9 ( collec­tions 28 and 98). Harris and Thomas record it from the zone of Diplograptus decoratus in the Middle Ordovician of Vic­toria, Australia. Section SCHIZOGRAPTI Genus TROCHOGRAPTUS Holm, 1881 TROCHOGRAPTUS LAPWORTHI Ruedemann Trochograptus lapworthi Ruedemann, 1947, Geo!. Soc. America Mem. 19, p. 294, pl. 47, figs. 18, 19. Remarks.-The Texas specimens agree closely with Ruedemann's specific descrip­tion. Horizon.-Specimens of this species were collected from one locality (collection 48) which is in zone 4 d the Marathon limestone. Ruedemann's types came from the lowest zone of the Levis shale at Point Levis, Quebec. The species ap­parently occurs in slightly younger beds in the Levis sequence than it does in the Marathon. Section DICHOGRAPTI Genus DICHOGRAPTUS Salter, 1863 DICHOGRAPTUS OCTOBRACHIATUS (Hall) Pl. 7, fig. 13; Pl. 8, figs. 2, 12 Graptolithus octobrachiatus Hall, 1858, Canada Geo!. Survey, Rept. Prog. for 1857, p. 122. Dichograptus octobrachiatus Elles and Wood, 1902, Mon. British Grapt., pp. 77-79, pl. 9, pl. 10, figs. la·e. Dichograptus octobrachiatus Ruedemann, 1947, Geo!. Soc. America Mem. 19, pp. 288-289, pl. 46, figs. 3-7. Remarks.-The Texas specimens agree well with the specific description by Rue­demann. The number of stipes that speci­mens of this species may have is not in­variable, and septad and hexad types have been noted. One specimen of the hexad type was found in zone 6 (collection 23) in the Marathon limestone. Horizon.-D. octobrachiatus is common in the upper part of the Marathon lime­stone, zones 3 (collection 80), 4 (collection 69) , 5 (collection 26) , and 6 (collections 23, 25, 114, and 115). Two specimens were found in the upper part of the Fort Peiia formation, zone 9 (collection 28). Ruedemann states that the species is com­mon in graptolite bed 2 (Tetragraptus zone) , rare in graptolite bed 3 (Didymo­graptus bifidus zone), and one specimen was found in the uppermost horizon with Dipwgraptus dentatus of the Deepkill shale in New York. Elles and Wood record the species from the Arenig, Middle Skiddaw slates in England. The species ranges through the Bendigo series into the Chew­ton series in the Lower Ordovician of Vic­toria, Australia. DICHOGRAPTUS MARATHONENSIS Berry, n. sp. Pl. 13, fig. 5 Description.-Stipes of the first order are 2 mm long and thus the funicle is 4 mm long. The second order stipes are equal Bureau of Economic Geology, The University of Texas in length to those of the first order and in· elude an angle of 100 to no degrees. These give rise to stipes of the third order which are up to 2.5 cm long. The stipes of the first and second orders are about 0.4 mm wide but the third order stipes widen rapidly from 0.5 mm to 1.2 mm in width, which width is then maintained. Thecae appear only on the third order stipes and number 8 to 9 in 10 mm, are in· clined at a 10-to 15-degree angle, are three times as long as they are wide, and overlap about one-third of their length. Remarks.-This form is close to D. nor· vegicus Harris and Thomas (1940, p. 130; pl. 1, figs. 4a-c; pl. 2, fig. 5) but differs from it in having slightly longer first and second order stipes (2.0 mm compared to 1.5 mm in D. norvegicus) and the thecae show a constant angle of inclination to the stipe of 10 to 15 degrees, while in D. nor­vegicus the angle of inclination increases toward the aperture of the thecae. Horizon.-This species is found in zone 9, the upper part of the Fort Pena forma­tion (collections 14 and 28). Holotype.-Yale Peabody Museum No. 20257. Section TETRAGRAPTI Genus TETRAGRAPTUS Salter, 1863 TETRAGRAPTUS ACCLINANS Keble Pl. 7, fig. 5 Tetragraptus acclinans Keble, 1920, Rec. Geol. Surv. Victoria, vol. 4, p. 198, text fig. 63, pl. 33, figs. 2a-c. Tetr<;igraptus acclinans Harris and Thomas, 1938, Mm. and Geo!. Journal, p. 69, pl. 1, fig. 16. Remarks.-The Texas specimens agree closely with Keble's specific description. Horizon .-Specimens of this species ~ere collected from zone 4 (collection 48) m the upper part of the Marathon lime­stone. Keble records it from the highest zone in the Lancefield series and the lowest zone of the Bendigo series in Victoria, Aus­tralia. The species occurs in the Marathon succession with the same associates (T. fruticosus, four-branched form, Didymo­graptus extensus, etc.) as it does in the Bendigo series in Australia. TETRAGRAPTUS AMII Lapworth Pl. 6, fig. 10; Pl. 7, fig. 9 Tetragraptus amii Lapworth MS, 1890. Tetragraptus amii Elles and Wood 1902 Mon. British Grapt., pp. 60-61, text fig. S6, pl. '5, figs. 4a-c. Tetragraptus amii Ruedemann, 1947, Geol. Soc. America Mem. 19, pp. 301-302 pl. 50 figs. 12-14. , • Remarks.-The Texas specimens are all small, but in shape of the rhabdosome, in number of thecae (10 in 10 mm) and in the character of the thecae, they agree with the description of T. amii by Elles and. Wood. The main stipes of the Texas spe­cimens are up to 2 cm in length and 2 mm in breadth, while Elles and Wood state that the main stipes are, as a rule, from 2.5 to 3.5 cm in length and 3 mm in width. They also state that a rapid increase in breadth near the initial extremity of the main stipes is characteristic and even the smaller forms which do not attain the maximum di­mensions have this feature. The Texas forms do show this rapid increase in breadth at the proximal extremity of the main stipes. The sicula is obscure in all of the Texas specimens. Horizon.-T. amii was collected from zones 4, 5, 6, of the upper part of the Mara· thon limestone (collections 26, 40, 69, and 71) and from low in zone 8 (collection 113) in the Alsate shale. Ruedemann found it in zone 2 ( T etragraptus zone) of thP. Deepkill shale in New York. Raymond (1914) lists it from his zone D-2 (Diplo­graptus dentatus zone) of the Levis shale of Quebec, and Miser and Purdue (1929) list it from the Mazarn shale in the Ouachita Mountains. Elles and Wood record the species from the Arenig, Middle Skiddaw slates in England. TETRAGRAPTUS APPROXIMATUS (Nlehobon) Pl. 6, figs. 1-3 Tetragrapsus approximatus Nicholson 1873 Ann Mag. Nat. Hist., se;. 4, vol. 11, p. 1,36, fi~. 2. · Tetragraptus approximatus Harris and Thomas 1938, Min. and Geol. lour., p. 74, pl. 1, figs'. l 7a-c, pl. 4, fig. 16. Tetragraptus (Etagraptus) approximatus Ruede· mann, 1947, Geol. Soc. America Mem 19 pp 312-313, pl. 52, figs. 4-6, 17, 18. · ' · Gre,rpwlite Faunas, Marathon Region Remarks.-The Texas specimens agree closely with the specific description by Ruedemann. From specimen to specimen, the stipes show a slight variation in curva· ture at their origin from the funicle, but in all, the stipes become subparallel to one another. Because the stipes do show vari· ation in curvature at their origin from the funicle, not all specimens form a perfect letter "H." Since Ruedemann gave the formation of a letter "H" by the second order stipes with the funicle as the distinc· tive character of the subgenus Etagraptus, the writer is of the opinion that the sub· generic category is not necessary, at least in the case of T. approximatus. Horizon.-T. approximatus is the char· acteristic species of zone 3 (collections 76, 80, 120, and 130) in the middle part of the Marathon limestone. The species has been chosen as the name-giver to that zone. T. approximatus is common in Raymond's (1914) zone A, the lowest beds of the Levis shale in Quebec. Also, the species is the characteristic form in the highest zone of the Lancefield series of the Lower Ordovi­cian in Victoria, Australia (Harris and Keble, 1932). It occurs in the Levis shale, in Marathon zone 3, and in the Lance­field zone 3, with the same associates (Clonograptus rigUlus, T etragraptus quad­ribrachiatus, etc.). TETRAGRAPTUS BIGSBY! (Hall) Pl. 7, fig. 11 Phyllograptus simili.s Hall, 1858, Canada Geol. Survey, Rept. Prog. for 1857, p. 140. Graptolithus bigsbyi Hall, 1865, Canadian Or· ganic Remains, p. 86, pl. 16, figs. 22-30. Tetragraptus bigsbyi Elles and Wood, 1902, Mon. British Grapt., pp. 68-69, text figs. 42a, b, pl. 6, figs. 6a-e. Tetragraptus similis Ruedemann, 1904, (pars) New York State Mus. Mem. 7, pp. 658-662, text figs. 58, 60, 61 (not fig. 59), p. 642, fig. 48, p. 644, fig. 49 (not fig. 50), pl. 12, figs. 3, 6, 9, 10, not figs. 2, 4, 5, 7. Tetragraptus bigsbyi Monsen, 1937, Norsk, Geol. Tiddsskr., Bd. 16, pp. 169-170, taf. 4, figs. 1, 2, 6, 10, 24, taf. 13, figs. 7, 8, 10, 11. Tetragraptus similis Ruedemann, 1947, (pars) Geol. Soc. America Mem. 19, p. 310, pl. 51, figs. 4, 5, 7, 11, not figs. 6, 8, 9, 10, 12, 13. Remarks.-The Texas specimens agree well with Hall's original description and with Elles and Woods' figures and descrip· tion. Hall (1858) originally placed these reclined tetragraptids under the genus Phyllograptus and gave them the specific name similis. Subsequently, Hall ( 1865) realized that such forms were not phyllo· graptids and removed them to the genus Graptolithus. Since he had already named a species Graptolithus similis, he gave the name G. bigsbyi to the forms originally called P. similis. Subsequently, the genus Graptolithus was split up to several genera including DUlymograptus and Tetragrap· tus, and Hall's G. similis then became D. similis. Ruedemann (1904) stated that since G. similis was now D. similis, the name T etragraptus similis would have priority over the name T. bigsbyi for the forms Hall originally named Phyllograptus similis. However, under the 1933 Rules of Nomenclature, Ruedemann was not correct in reviving a name which had been dropped. Other authors (Holm, 1895; Elles and Wood, 1902; Monsen, 1937; and Bulman, 1955) have followed Hall's ( 1865) usage, and this writer proposes to do so here. Further, Ruedemann (1904, pl. 12, figs. 2, 4, 5, and 7, and 1947, pl. 51, figs. 6, 8, 9, 10 12, and 13 ) included forms under T. similis not like Hall's description. These forms should be referred to the species T etragraptus serra. Horizon.-Specimens of T. bigsbyi were collected from the middle and upper parts of the Marathon limestone, zones 3 ( collec· tion 120) , 4 (collection 71) , 5 (collection 26) , 6 (collections 25, 40, 52, 63, 64, and 115) , and 7 (collection 4 7) . Hall's original material came from the Levis shale in Quebec, and Raymond (1914) lists it from his zones C-2, C-3, and D-1 (Didymograp­tus bifidus and lower Diplograptus denta· tus zones) of that shale. Ruedemann re­cords the species from graptolite zone 1 (T etragraptus zone) of the Deep kill shale in New York. Elles and Wood state that the species occurs in abundance in the lower part and ranges into the middle part of the Skiddaw slates (zones of DUlymograptus extensus and D. hirundo) in the British Isles. Benson and Keble ( 1935) report the Bureau of Economic Geology, The University of Texas form from New Zealand, and Harris and Keble (1932) show the species ranging through the Bendigo and Chewton series in Victoria, Australia. The species occurs in similar assemblages in both the Victo· rian and Marathon successions. TETRAGRAPTUS DECIPIENS T. S. Hall Pl. 5, fig. 4 Tetragraptus decipiens T. S. Hall, 1899, Royal Soc. Victoria, Proc. (n.s.), vol. 11, pp. 168­ 169, pl. 17, figs. 13-15, pl. 18, figs. 16--19. Remarks.-The Texas specimens agree with T. S. Hall's specific description ex­cept that the outer margins of the thecae are straight, and the thecae maintain their low angle of inclination to the stipe throughout, while in the Australian ma­terial the outer margins of the thecae have a concave curvature which increases near the aperture. Horizon.-Specimens of T. decipiens were collected from the lower part of the Marathon limestone, zone 2 (collections 72E and 84). Harris and Keble (1932) list T. decipiens with Adelograptus vic­toriae as characteristic species of the sec­ond zone in the Lancefield series of the Lower Ordovician in Victoria, Australia. T. decipiens occurs with the same associ­ ates in both the Victorian and Marathon sequences. TETRAGRAPTUS DECIPIENS var. BIPATENS Keble and Harris Tetragraptus decipiens var. bipatens Keble and Harris. 1934, Nat. Mus. Melbourne, Mem. 8, pp. 170--172, text figs. 2, 3. Remarks.-The Texas specimens agree well with the specific description by Keble and Harris. Horizon.-Specimens of this species were collected from one locality (collection 22) which is in zone 6 in the upper part of the Marathon limestone. Keble and Har­ris record the species from the lower part of the Bendigo series of the Australian Lower Ordovician. The species occurs slightly higher in the Marathon sequence than in the Victorian. TETRAGRAPTUS FRUfICOSUS (Hall) Pl. 6, figs. 7, 11, 12; Pl. 7, fig. 14; Pl. 8, figs. 1, 3; Pl. 9, fig. 3 Graptolithus fruticosus Hall, 1858, Canada Geol. Survey, Rept. Prog. for 1857, p. 128. Graptolites (Didymograptus) fruticosus McCoy, 1874, Geo!. Survey Victoria, Prodr. Pal. Vic­ toria, dee. 1, p. 13, pl. l, figs. 9-14. Tetragraptus fruticosus Elles and Wood, 1902, Mon. British Grapt., pp. 61-63, text fig. 37, pl. 6, figs. 2a, b. Tetragraptus fruticosus Ruedemann, 1947, Geol. Soc. America Mem. 19, pp. 304-305, pl. 51, figs. 25-32. Remarks.-Two forms of this species are present in the Marathon succession. The two forms are alike in all essential characters except that in one, the normal four stipes are present, while in the other, one of the two secondary stipes does not develop, giving rise to a 3-branched form. Small 4-branched forms in which the stipes are rarely more than 15 mm in length appear first in the sequence, then larger 4-branched rhabdosomes in which the stipes are strongly curved and are up to 12 cm in length come in. The 3-branched rhabdosomes appear later than the small 4-branched forms but appear with the ro· bust 4-branched forms. The 3-branched forms are not so robust as the large 4­branched forms, since their stipes meas­ure only 3 to 4 cm in length and up to 3 mm in breadth. Horizon.-T. fruticosus is a common species in the upper part of the Marathon limestone. The 4-branched form is the characteristic element of zone 4 (collec­tions 4, 69, 71, and 101) and it ranges up into zones 5 (collections 26, 27, and 90) and 6 (collections 23, 114, and 115). The 3-branched form is the characteristic ele­ment of zone 5 (collections 26, 27, and 90), and it ranges into zone 6 (collections 23, 24F, 25, 40, 52, 63, 64, 65B, and 115) where it is very common. Ruedemann re­cords the species from graptolite beds 1 and 2 ( T etragraptus zone) of the Deepkill shale in New York. Raymond (1914) lists it from his zone B of the Levis shale in Quebec. Elles and Wood report the species only from the Arenig rocks (zone of Didy­mograptus extensus) of the Girvan district Graptolite Faunas, Marathon Region in South Scotland. The 4-and 3-branched varieties were among the first graptolites recognized in Australia (McCoy, 1874). Harris and Thomas ( 1938b) show that the subdivision of the Bendigo series in Vic­toria Australia is based on the introduc­tion ~f the 4-b;anched form, then the ap­pearance of the 3-branched form with the 4-branched form, and, finally, the loss of the 4-branched form with the 3-branched form remaining. The sequence of appear­ances of the two forms of this species is the same in both the Victorian and Marathon successions. Further, the species is associ­ated with the same tetragraptids and didy­mograptids in both successions. TETRAGRAPTUS PENDENS Elles Pl. 7, fig. 7 Tetragraptus pendens Elles, 1898, Geo!. Soc. Lon­don, Quart. Jour., vol. 54, p. 491, fig. 13. Tetragraptus pendens Elles and Wood, 1902, Mon. British Grapt., pp. 63-64, text fig. 38, pl. 6, figs. 3a-d. Tctragraptus pendens Ruedemann, 1947, Geo!. Soc. America Mem. 19, pp. 306-307, pl. 51, figs. 18-21. Remarks.-The Texas specimens of this characteristic slender species agree with Elles' description. Horizon.-A few specimens of this species were collected from zone 4 of the Marathon limestone. They were identified in collection 71. Ruedemann recorded the species from the zone of Didymograptus bifidus of the Deepkill shale in New York and Raymond (1914) listed it from the same zone in the Levis shale in Quebec. Elles and Wood record it from the Arenig, Middle Skiddaw slates in England. Har­ris and Thomas ( 1938b) and Harris and Keble (1932) report T. pendens in the Bendigo series and ranging into the Chew­ton series in Victoria, Australia. The form appears slightly earlier (in the 4-branched T etragraptus fruticosus zone) in Australia and in the Marathon region than it does in New York and Quebec. TETRAGRAPTUS PYGMAEUS Ruedemann Tetragraptus pygmaeus Ruedemann, 1904, New York State Mus. Mem. 7, pp. 664-665, pl. 12, figs. 11-14. Tetragraptus pygmaeus Ruedemann, 1947, Geol. Soc. America Mem. 19, p. 307, pl. 51, figs. 14­ 17. Remarks.-The Texas specimens agree well with Ruedemann's specific description. Horizon.-Specimens of T. pygmaeus were obtained from zones 5 and 6 of the upper part of the Marathon limestone (col­lections 25, 40, and 90). Ruedemann states that this species is quite common in grap­tolite bed 2 (Tetragraptus zone) of the Deepkill shale in New York and is rare in beds with Diplograptus dentatus at Mt. Merino, New York. TETRAGRAPTUS QUADRIBRACHIATUS (Hall) Pl. 7, fig. 12 Graptolithus quadribrachiatus Hall, 1858, Can­ ada Geo!. Survey, Rept. Prog. for 1857, p. 125. Tetragraptus quadribrachiatus Ruedemann, 1947, Geol. Soc. America Mem. 19, pp. 307­ 308, pl. 50, figs. 15-18. Remarks.-The Texas specimens agree fully with the description by Ruedemann. Horizon.-This species has one of the longest ranges of any graptolite. Further, it is one of the earliest tetragraptids to ap­pear and the last to drop out-ranging from zone 3 through zones 4, 5, 6, 7, 8, and into zone 9. It occurs in the upper part of the Marathon limestone, in the Alsate shale and in all but the highest beds of the Fort Pena formation and was identified in the following collections-13, 14, 15, 25, 26, 28, 30, 40, 40A, 47, 48, 52, 65B, 69, 71, 95, 98, 110, 111, 114, 120, and 121. Ruedemann records it from the Tetragrap­tus zone of the Deepkill shale and with Diplograptus dentatus near Mt. Merino, New York. Raymond (1914) lists it from zones A, B, and D-2 of the Levis shale in Quebec. Miser and Purdue ( 1929) list it from the Mazarn shale in the Ouachita Mountains. In Great Britain, the species occurs in the middle and upper beds of the Middle Skiddaw slates. Harris and Keble ( 1932) list the species as ranging from the highest zone of the Lancefieldian series (zone of Tetragraptus approxima· tus) through Bendigo, Chewton, and Y apeen series into the lower part of the Middle Ordovician of Victoria, Australia. Bureau of Economic Geology, The University of Texas TETRAGRAPTUS RECLINATUS Elles and Wood Tetragraptus reclinatus Elles and Wood, 1902, Mon. British Grapt., p. 67, text fig. 41, pl. 6, figs. Sa-e. Remarks.-The Texas specimens agree well with Elles and Wood's specific descrip­tion. T. reclinatus resembles T. serra in shape but can be easily distinguished be­cause the stipes are much thinner (never more than 2.0 mm in T. reclinatus com· pared to 3.0 to 3.2 mm in T. serra) and the thecae more numerous per 10 mm ( 12 to 13 in T. reclinatus and 8 to 10 in 10 mm in T. serra) . Horizon.-Specimens of T. reclinatus were collected from zone 6 (collections 25 and 63) in the upper part of the Marathon limestone. Elles and Wood record the species from the Arenig, middle part of the Skiddaw slates. C. E. Decker (personal communication) found some poorly pre· served specimens of the species in the West Spring Creek limestone of the Arbuckle group in the Arbuckle Mountains, Okla­homa. TETRAGRAPTUS SERRA (Brongnlart) Pl. 6, fig. 6; Pl. 13, fig. 1 Fucoides serra Brongniart, 1828, Hist. Veget. Foss., p. 71, pl. 6, fig. 7, 8. Tetragraptus serra Elles and Wood, 1902, Mon. British Grapt., pp. 65-67, text figs. 40a-c, pl. 6, figs. 4a-f. Tetragraptus serra Ruedemann, 1947, Geol. Soc. America Mem. 19, pp. 309-310, pl. 50, figs. 19­ 23. Remarks.-The Texas specimens are all immature but agree well with the specific description by Elles and Wood except that the thecae number 9 to 10 in 10 mm while they number 8 to 9 in 10 mm in the British material. However, in the figures of T. serra in the Elles and Wood monograph, the thecae number 9 to 10 in 10 mm near the proximal end, and this is the same re­ gion in which the thecal measurements were made on the Texas specimens. Horizon.-Specimens of T. serra were collected from the upper part of the Mara~ thon limestone, zones 5, 6, and 7 ( collec­ tions 25, 26, 47, 52, and 63), and the mid­ dle part of the Fort Pena formation, zone 9 (collection 28) . Brongniart' s original material came from Point Levis, Quebec, and several authors cite the occurrence of this species there. Raymond ( 1914) lists it from his zones A, C-2, and D-2 of the Levis shale. Ruedemann records it from zone 1 (the T etragraptus zone) of the Deep kill shale in New York. Elles and Wood report T. serra to be very abundant in the upper beds of the Arenig, Skiddaw slates where it occurs with T. amii and Didymograptus extensus. Harris and Thomas ( l 938b) fig­ure T. serra as one of the most characteris­tic forms in the Bendigo series in Victoria, Australia. Harris and Keble (1932) show the species ranging through the Bendigo, Castlemaine, and what is now the Y apeen series in Victoria. T. serra has the same associated species and the same range in both the Marathon and Victorian se­quences. TETRAGRAPTUS TARAXACUM Ruedemann Pl. 8, fig. 13 Tetragraptus taraxacum Ruedemann, 1902, New York State Mus. Bull. 52, p. 589, fig. 16. Tetragraptus taraxacum Ruedemann, 1947, Geol. Soc. America Mem. 19, p. 311, pl. 50, figs. 24­ 29. Remarks.-The Texas specimens agree fully with Ruedemann's specific descrip­tion. Horizon.-The specimens of T. taraxa­cum were collected from zones 3, 5, and 6 in the upper part of the Marathon lime· stone (collections 52, 64, 90, and 120). Ruedemann states that the majority of his specimens were obtained from graptolite bed 2 of the Deepkill shale ( T etragraptus zone) but a few were also observed in the beds with Glytograptus dentatus at Mt. Merino, New York. Genus PHYLLOGRAPTUS Hall, 1858 PHYLLOGRAPTUS ANGUSTIFOLIUS Hall Phyllograptus angusti/olius Hall, 1858, Canada Geol. Survey, Rept. Prog. for 1857, p. 139. Phyllograptus angusti/olius Elles and Wood, 1902, Mon. British Grapt., pp. 100-101, text fig. 59, pl. 13, figs. 7a-f. Phyllograptus angusti/olius Ruedemann, 1947, Geol. Soc. America Mem. pp. 315-316, pl. 53, figs. 2-6. Grapwlite Faunas, Marathon Region Remarks.-The Texas specimens agree fully with the description by Elles and Wood. Horizon.-This species was collected from zones 5 and 6 in the upper part of the Marathon limestone (collections 26, 40, 52, and 63). Ruedemann records the species from all three zones of the Deepkill shak in New York. Hall's types came from the Levis shale in Quebec. Elles and Wood state that P. angustifolius is an abundant form in the Skiddaw slates where it has a fairly long range. Harris and Thomas ( 1938b) include it as a common species in the Bendigo series in Victoria, Australia. PHYLLOGRAPTUS ANNA Hall PL 8, fig. 14; Pl. 10, fig. 4 Ph~·llograptu.s anna Hall, 1865, Canadian Organic Remains, p. 124, pl. 16, figs. 11-16. Phyllcgraptu.s anna Elles and Wood, 1902, Mon. British Grapt., pp. 101-102, text figs. 60a-b, pl. 13, figs. 6a-f. Phyllograptu.s anna Ruedemann, 1947, Geo!. Soc. America Mem. 19, pp, 316-317, pl. 53, figs. 27­ 32. Remarks.-The Texas specimens agree folly with the description by Ruedemann. Horizon. -Ruedemann (in Sellards, 1933) first reported P. anna from the Marathon limestone. The writer collected it from zones 5. 6, and 7 in the upper part of that formation (collections 20, 23, 25, 26, 40A, 47, 52, 63, 65A, 65C, 67, and l15). Tiuedemann records the species from the "last layers of graptolite bed 2" (Tetra­graptus zone) , throughout the horizon with Didymograptus bifidus (zone 2), and from zone 3 bed 1 (zone of Diplograptus den­tatus) of the Deepkill shale in New York. Raymond (1914) listed the species from zone C-3 (zone of D. bifidus) of the Levis shale in Quebec. Elles a.nd Wood report it from the middle part of the Skiddaw slates in the British Isles. PHYLLOGRAPTUS A..'\"'\'A mot. LONGUS Ruedemann Pl. 8, fig. 16 Phyllograptu.s anna Hall mut. lcngu.s Ruedemann, 1947, Geol. Soc. America Mem. 19, p. 317, pl. 53, figs. 36-40. Remarks.-The Texas specimens agree closely with Ruedemann's description. Horizon.-Specimens of this variety were collected from one locality (collection 25) which is in zone 6 in the upper part of the Marathon limestone. Ruedemann's type material came from the Glenogle shale in British Columbia. PHYLLOGRAPTUS ILICIFOLIUS Hall Pl. 8, fig. 4; PL 9, figs. 1, 2 Phyllograptu.s ilici/olius Hall, 1858, Canada Geo!. Survey, Rept. Prog. for 1857, p. 139. Phyllograptus ilici/olius Ruedemann, 1947, Geo!. Soc. America Mem. 19, pp. 317-318, pl. 53, figs. 9-19. Remarks.-The Texas specimens agree fully with the specific description by Ruedemann. Horizon.-P. ilicifolius is a common fos­sil in zones 4 (collection 71) , 5 (collection 26). 6 (collections 23, 25, 30, 40, 40A, 52, and 115), and 7 (collections 19 and 20) in the upper part of the Marathon lime­stone. The species is very common in zone 1 ( T etragraptus zone) bed 2 and rare in zone 1 bed 1 and in zone 2 (Didymograp­tus bi.fidus zone) of the Deepkill shale in New York. Raymond (1914) lists it from his zones A, C-1, C-2, and C-3 of the Levis shale in Quebec. Ruedemann records it from many other localities in North America, and Harris and Thomas ( 1938h) figure it as one of the characteristic species in the Bendigo series in Victoria, Aus­tralia. PHYLLOGRAPTUS NOBILIS Harris and Keble Pl. 14, figs. 6, 7 Phyllograptu.s nobilis Harris and Keble, 1932, Royal Soc. Victoria, Proc. ( n.s.), vol. 44, p. 41, pl. 6, figs. 3, 4. Remarks.-The Texas specimens agree fully with the specific description by Harris and Kehle. Horizon.-Specimens of P. nobilis were· collected from hut one locality (collection 85) which is in the highest beds of the Fort Pena formation, zone 10. Harris and Kehle's type specimens came from the upper part of the Middle Ordovician in Victoria, Australia, and Harris ( 1935) lists the species as very common in the zone of Dipfugraptus (Mesograptus} decoratus Bureau of Economic Geology, The University of Texas of the Middle Ordovician of the Victorian sequence. PHYLLOGRAPTUS TYPUS Hall Pl. 10, figs. 1, 11, 13 Phyllograptus typus Hall, 1858, Canada Geol. Survey, Rept. Prog. for 1857, p. 137. Phyllograptus cf. typus Elles and Wood, 1902, Mon. British Grapt., pp. 99-100, text fig. 58, pl. 13, figs. Sa, b. Phyllograptus typus Ruedemann, 1947, Geo!. Soc. America Mem. 19, pp. 320-321, pl. 53, figs. 22­ 26. Remarks.-Rhabdosomes of this species are highly variable in length and width. The British forms are slightly larger than the American types described by Hall. The British specimens vary in form from long and narrow with maximum dimensions of 57 mm in length and 6.3 mm in width to shorter and broader forms with dimensions of 25.4 mm in length and 8.7 mm in width. Ruedemann states that the Ameri­can material does not reach these extremes in dimensions, but one form figured by Hall measures 56 mm in length and 17 mm in width, and a specimen from the Levis shale figured by Ruedemann measures 55 mm in length and 17 mm in width. The specimens from the Marathon region were measured, and the size range was from forms 15 mm in length and 0.9 mm in width to forms 35 mm in length and 16 mm in width. The mean length of the speci­mens was 20.4 mm and the mean width 10.l mm. The Texas specimens are shorter and broader than the British material, but they compare favorably in form ratio with specimens from the Deepkill shale in New York. In the curved character of the thecae, in the number of thecae (9 to 10 per 10 mm), and in the slightly mucronate aper­tures, the Texas specimens agree with the specific description by Ruedemann. Horizon.-Ruedemann (1947, p. 321) states that he had "undoubted specimens of this species" from the Marathon region. The writer collected it from the upper part of the Marathon limestone, zones 6 and 7 (collections 47, 63, 65C, 65D, 67, and 70) and from the Alsate shale and lower part of the Fort Pena formation, zone 8 ( collec­tions 113 and 141). The species is common in zone 7 but is rare in the zones above and below. Ruedemann records the species from graptolite bed 3 (zone of Didymo­graptus bifidus) of the Deepkill shale in New York. Raymond (1914) lists it from zone B of the Levis shale in Quebec. Ruedemann also records it from the Glen­ogle shale in British Columbia associated with a fauna similar to that of zone 8 in the Marathon succession. The forms Elles and Wood referred to P. typus came from the Arenig, Middle Skiddaw slates in Scot­land and Wales. Harris and Thomas ( l 938b) figure a form tentatively referred to P. typus as a characteristic element of the fauna of the Castlemaine series in Vic­toria, Australia. Section DIDYMOGRAPTI Genus DIDYMOGRAPTUS McCoy (In Sedgwick and McCoy, 1851) DIDYMOGRAPTUS AFFINIS (Nicholson) Didymograpsus a/finis Nicholson, 1869, Ann. Mag. Nat. Hist., ser. 4, vol. 4, p. 240, pl. 11, fig. 20. Didymograptus a/finis Elles and Wood, 1901, Mon. British Grapt., pp. 23-24, text figs. 13a, 13b, pl. 2, figs. la-b. Remarks.-The stipes of the Texas specimens are not more than 0.5 mm wide and diverge at an angle of 160 degrees from the sicula, whereas in the British specimens the stipes are 0.6 mm wide and diverge at an angle of 90 to 150 degrees. In all other respects the Texas specimens agree with the description of the British material by Elles and Wood. Horizon.-D. a/finis was collected from the Alsate shale (collections 8 and 113) in the lower part of zone 8. The species has been recorded from the Glenogle shale (Ruedemann, 1947) and from the Arenig, middle and upper part of the Skiddaw slates in the British Isles. DIDYMOGRAPTUS ARTUS Elles and Wood Pl. 10, figs. 2, 5, 6 Didymograptus artus Elles and Wood, 1901 Mon. British Grapt., p. 48, text fig. 30, pl. 4, figs. 6a-d. Didymograptus artus Ruedemann, 1947, Geol. Soc. America Mem. 19, p. 326, pl. 54, figs. 3-10. Grapwlite Faunas, Marathon Region Remarks.-The Texas specimens agree well with Elles and Wood's description. Horizon.-D. artus is a diagnostic spe­cies of zone 7, the highest in the Marathon limestone, and it is restricted to that zone. It was identified in collections 19, 24A, 24B, and 47. Ruedemann (1947) records the species from the Black Rock lime­stone in Arkansas and the Joins lime­stone in the Arbuckle Mountains in Okla­homa. Elles and Wood report the species in the upper part of the Skiddaw slates where it is a diagnostic form of the zone of Didymograptus bifidus. The species has not been reported from Australia; its ap· pearance in the Marathon succession with a predominantly Australian graptolite se­quence affords a tie point between the British and Australian zonal schemes. DIDYMOGRAPTUS BIFIDUS (Hall) PI. 10, figs. 3, 7-10 Graptolithus bi/idus Hall, 1865, Canadian Organic Remains, p. 73, pl. 1, figs. 16-18, pl. 3, figs. 9-10. Didymograptus bifidus Elles and Wood, 1902, Mon. British Grapt., pp. 42-44, text figs. 26a, b, pl. 4, figs. la-f. Didvmograptus bifidus Ruedemann, 1947, Geo!. Soc. America Mem. 19, pp. 327-328, pl. 54, figs. 11-16. Remarks.-The Texas specimens are all small, and although numerous specimens were collected from several localities, many are immature. The character and number of the thecae, the size of the sicula, and the variation in angle of divergence of the stipes agree with the description given by Ruedemann. The length of the mature forms ranges from 1.2 to 2.2 cm and the width from 2.0 to 2.4 mm. Although none of the Texas specimens attained the di­mensions of Hall's largest forms, some do fall within the range of variation of the dimensions given by both Elles and Wood and by Ruedemann; therefore some speci­mens of adult forms of D. bifidus appear to be present. Associated with D. bifidus in the lower part of zone 7 are several transient forms between D. bifidus and D. prowbifidus which are very close to D. bifidus. The transients have thinner stipes and fewer thecae per 10 mm than the true D. bifidus. Horizon.-Ruedemann (in Sellards, 1933) first recorded D. bifidus from the Marathon limestone. It is the most diag· nos tic fossil of zone 7, the uppermost 30 feet of the Marathon limestone. The species is common and widespread in the zone, and it was identified in the following col­lections: 9, 19, 20, 24A and B, 47, 65D, 67, and 70. D. bifidus is the characteristic ele­ment of zone 2 of the Deepkill shale in New York and of Raymond's (1914) zones C-2 and C-3 of the Levis shale in Quebec. The species is widely distributed in the lower part of the Llanvirn series in the British Isles, and it marks the sixth zone of the British sequence. DIDYMOGRAPTUS COMPRESSUS Harris and Thomas Didymograptus compressus Harris and Thomas, 1935, Royal Soc. Victoria, Proc. (n.s.), vol. 47, pp. 293-294, fig. l, nos. 6a-c, fig. 2, nos. 20, 21. Remarks.-The Texas specimens agree closely with the specific description by Harris and Thomas. Horizon.-Specimens of this species were collected from the upper part of the Fort Pefia formation, zone 9 (collection 28). Harris and Thomas (1935) report the species to be common in the zone of Glyptograptus intersitus and to be rare in the zone below (zone of Glyptograptus austrodentatus) in the Middle Ordovician of Victoria, Australia. D. compressus oc­curs with the same associates (G. inter­situs, G. austrodentatus, Trigonograptus ensiformis, Didymograptus nodosus, etc.) in both the Marathon and Victorian se­quences. DIDYMOGRAPTUS CUSPIDATUS Ruedemann Didymograptus cuspidatus Ruedemann, 1904, New York State Mus. Mem. 7, p. 698, text fig. 90, pl. 15, figs. 8, 9. Didymograptus cuspidatus Harris and Thomas, 1935, Royal Soc. Victoria, Proc. ( n.s.), vol. 47, p. 293, fig. 1, no. 9, fig. 2, nos. 11, 12. Didymograptus cuspidatus Ruedemann, 1947, Geol. Soc. America Mem. 19, p. 330, pl. 55, fig. 2, pl. 56, fig. 19. Remarks.-The sicula is short and in­conspicuous, and the stipes originate sub­ Bureau of Economic Geology, The University of Texas orally from it at different levels and di­verge initially at an angle of 140 to 160 degrees, but later they become sub-hori­zontal. The stipes are 2.0 cm or more long and are narrow (0.4 mm) at first but widen to 1.0 mm. The thecae number 12 to 13 in 10 mm and the mature ones overlap about one-third their length. The inclina­tion of the early thecae is about 20 degrees but increases to 40 degrees in the apertural part of the later thecae. The apertural margins are slightly convex and approxi­mately normal to the axis of the stipe. The above description of the Texas specimens agrees well with Ruedemann's description based on a single specimen. Horizon.-D. cuspidatus was collected from the Fort Pena formation, zones 8 (collection 61B) and 9 (collections 14, 16, and 98). Ruedemann's type came from the shales with Diplograptus dentatus at Mt. Merino, New York. Harris and Thomas record it from the zone of Diplograptus decoratus of the Middle Ordovician in Vic­toria, Australia. The species occurs with the same associates (Hallograptus ethe­ridgei, Cryptograptus schaferi, and Didy­mograptus nodosus) in both the Marathon and Victorian sequences. DIDYMOGRAPTUS DENTICULATUS Berry, n. sp. Pl. 10, fig. 12 Description.-The stipes diverge initi­ally at about a 90-degree angle, then in­curve and become subparallel. They widen from 0.8 to 1.5 mm in the first 5 mm, then increase in width gradually to a maximum of 1.8 mm. The stipes are 1. 7 cm in length. The thecae number 7 in 10 mm, overlap one-half their length, are three times as long as they are wide, and are inclined at a 35-to 45-degree angle to the stipe. The apertural margins are concave and have distinct mucros. Horizon.-Specimens of this species were collected from one locality only (col­lection 20) , which is in the uppermost part of the Marathon limestone, zone 7. Holotype.-Yale Peabody Museum No. 20252. DIDYMOGRAPTUS ELLESAE Ruedemann Didymograptus ellesi Ruedemann, 1904, New York State Mus. Mem. 7, pp. 682-{)83, text figs. 75, 76, pl. 14, figs. 22-24. Didymograptus ellesae Ruedemann, 1908, New York State Mus. Mem. 11, p. 134. Didymograptus ellesae Ruedemann, 1947, Geol. Soc. America Mem. 19, pp. 330-331, pl. 55, figs. 8-10, pl. 56, fig. 15. Remarks.-The Texas specimens agree closely with Ruedemann's description. Horizon.-Specimens of this species were collected from one locality ( collec­tion 48) where they were associated with Didymograptus extensus, T etragraptus ac­clinans, and Tetragraptus quadribrachi­atus. The locality is in zone 4, in the upper part of the Marathon limestone. Ruede­mann obtained his type material from graptolite bed 3 (D. bifidus zone) of the Deepkill shale in New York. DIDYMOGRAPTUS EUODUS Lapworth Didymograptus euodus Lapworth, 1875, Geol. Soc. London, Quart. Jour., vol. 31, p. 645, pl. 35, figs. la-c. Didymograptus euodus Elles and Wood, 1901, Mon. British Grapt., pp. 21-22, text fig. 12, pl. 1, figs. lOa-b. Didymograptus euodus Ruedemann, 1947, Geol. Soc. America Mem. 19, pp. 332-333, pl. 55, figs. 33-36, pl. 56, figs. 22-24. Remarks.-The Texas specimens agree with the description by Elles and Wood except that the stipes attain a width of 2.2 mm while the British specimens are 2.4 mm in width. Horizon.-D. euodus was collected from the lower part of the Fort Pena formation, zone 8 (collection 110). Ruedemann has recorded the species from the Blakely sand­stone in the Ouachita Mountains in Arkan­sas and the upper part of the Glenogle shale in British Columbia. Elles and Wood state that the species is known in the British Isles only from the zone of Didymograptus murchisoni in the Llanvirn series. DIDYMOGRAPTUS EXTENSUS (Hall) Pl. 6, fig. 5; Pl. 8, fig. 10 Graptolithus extensus Hall, 1858, Canada Geol. Survey, Rept. Prog. for 1857, p. 132. Didymograptus extensus Elles and Wood, 1901, Mon. British Grapt., pp. 8-9, text figs. 4a-d, pl. 1, figs. la, b. Graptolite Faunas, Marathon Region Didymograptus extensus Ruedemann, 1947, Geo!. Soc. America Mem. 19, pp. 331-332, pl. 55, fig. 16, pl. 56, figs. 1, 2. Remarks.-The Texas specimens agree well with the specific description by Ruede­mann. Horizon.-D. extensus is a common species in zones 3, 4, 5, and 6 (collections 21,23, 25,26, 27,32,40,48, 52,65C,66, 79, 90, 91, and 115), ranging from the middle of the Marathon limestone to near the top of it. Hall obtained the type ma­terial from the Levis shale in Quebec, and Raymond ( 1914) lists it in his zone C-2 of that formation. Ruedemann found it in bed 2 ( T etragraptus zone) of the Deepkill shale and Elles and Wood record it from the middle part of the Skiddaw slates of the Lake District and several other localities. Harris and Keble (1932) show the species ranges from the upper part of the Bendigo series, zone of T etragraptus fruticosus (3­and 4-branched forms) through the Chew­ton series in Victoria, Australia. DIDYMOGRAPTUS LEPTOGRAPTOIDES Monsen Didymograptus leptograptoides Monsen, 1937, Norsk. Geo!. Tidsskr., Bd. 16, pp. 136-138, taf. 2, figs. 3, 4, 32, 57, 63, 67, taf. 9, fig. 2. Remarks.-The Texas specimens agree closely with Monsen's specific description. Horizon.-The specimens of D. lepta· graptoides were collected from one locality only (collection 115) which is in zone 6 in the upper part of the Marathon lime­stone. Monsen's types came from the zone of Phyllograptus densus of the lower Didy­mograptus shales in Norway. DIDYMOGRAPTUS MENDICUS Keble and Harris Pl. 11, fig. 3 Didymograptus mendicus Keble and Harris, 1934, Nat. Mus. Melbourne Mem. 8, pp. 168-169, pl. 20,fig. 2. Remarks.-The Texas specimens agree fully with the specific description by Keble and Harris. Horizon.-Specimens of D. mendicus were collected from the Alsate shale (col­lection 113) which is the lower part of zone 8. Keble and Harris record the species from beds now included in the Chewton series in Victoria, Australia. DIDYMOGRAPTUS NICHOLSONI Lapworth Didymograptus nicholsoni Lapworth, 1875, Geo!. Soc. London, Quart. Jour., vol. 31, p. 644, pl. 33, figs. Sa-d. Didymograptus nicholsoni Elles and Wood, 1901, Mon. British Grapt., pp. 27-28, text figs. 16a-c, pl. 2, figs. 4a-c. Didymograptus nicholsoni Ruedemann, 1947, Geol. Soc. America Mem. 19, pp. 338-339, pl. 55, figs. 26-28, pl. 56, fig. 7. Remarks.-The Texas specimens agree fully with the specific description by Elles and Wood. Horizon.-Ruedemann (in Sellards, 1933) first listed D. nicholsoni from the Marathon limestone. The writer collected specimens of the species from zones 4, 5, and 6 of the upper part of the Mara­thon limestone (collections 39, 66, 68, and 115). Ruedemann records the species from Newfoundland as well as Marathon, Texas. Elles and Wood report it to be present in the middle and upper parts of the Skiddaw slates and to range into the zone of D. bi­fidus (low Llanvirn). Harris (1935) listed D. nicholsoni from the Bendigo series in Victoria, Australia. DIDYMOGRAPTUS NICHOLSONI var. PLANUS Elles and Wood Didymograptus nicholsoni var. planus Elles and Wood, 1901, Mon. British Grapt., p. 29, text figs. l 7a, b, pl. 2, figs. Sa, b. Didymograptus nicholsoni var. planus Ruede­mann, 1947, Geo!. Soc. America Mem. 19, p. 339, pl. 55, figs. 23-25, pl. 56, figs. 8, 9. Remarks.-The Texas specimens agree closely with Elles and Wood's description. Horizon.-A few specimens only of this variety were collected from zones 4 and 5 in the upper part of the Marathon lime­stone (collections 26, 69, and 90). Ruede­mann records the variety from zone 1 (the T etragraptus zone) of the Deepkill shale in New York and from the Glenogle shale in British Columbia. Elles and Wood's type specimens came from the upper part of the Skiddaw slates. DIDYMOGRAPTUS NITIDUS (Hall) Pl. 8, fig. 11 Graptolithus nitidus Hall, 1858, Canada Geol. Survey, Rept. Prog. for 1857, p. 129. Bureau of Economic Geology, The University of Texas Didymograptus nitidus Elles and Wood, 1901, Mon. British Grapt., pp. 10-11, text fig. 5a-d, pl. 1, figs. 2a-e. Didymograptus nitidus Ruedemann, 1947, Geol. Soc. America Mem. 19, pp. 339-340, pl. 55, figs. 11-14, pl. 56, fig. 21. Remarks.-The Texas specimens agree closely with the specific description by Ruedemann. Horizon.-Ruedemann (in Sellards, 1933) first listed D. nitidus from the Mara­thon limestone. The writer collected speci­mens of the species from several localities in zones 3, 4, 5, and 6 of the middle and upper parts of the Marathon limestone (collections 26, 36, 39, 66, 68, 69, 71, 79, 90, 91, and 101). Ruedemann found the species in graptolite beds 1 and 2 (Tetra­graptus zone) of the Deepkill shale in New York. Raymond (1914) lists it from zone C-1 of the Levis shale in Quebec and Miser and Purdue (1929) list it from the Mazarn shale in the Ouachita Mountains in Arkan­sas. Elles and Wood state that the form is widely distributed in the middle part of the Skiddaw slates in the British Isles, and Harris and Keble ( 1932) show it ranges through the Bendigo and beds now placed in the Chewton series in Victoria, Aus­tralia. DIDYMOGRAPTUS NODOSUS Harris Pl. 12, fig. 3 Didymograptus nodosus Harris, 1926, Royal Soc. Victoria, Proc. (n.s.), vol. 38, p. 56, pl. 1, figs. 1-4. Didymograptus nodosus Harris and Thomas, 1935, Royal Soc. Victoria, Proc. (n.s.), vol. 47, p. 295, fig. 2, no. 27. Remarks.-The Texas specimens of this species are poorly preserved, but they agree in all characters with the specific descrip­tion by Harris (1926). The species is char­acterized by distinctive thecae which are curved tubes arranged so that each arises from the preceding theca about halfway along its dorsal margin, then runs parallel with that theca and continues beyond its aperture. The apertural margins are straight and make an acute angle with the axis of the stipe. The stipes are marked by small trumpet-shaped promontories which are formed by the aperture of one theca and the heel of its successor. The Texas specimens do not show the thecal spines which Harris and Thomas ( 1935) de­scribed on some specimens of this species. Horizon.-Specimens of D. nodosus were collected from the upper part of the Fort Peiia formation, zone 9 (collections 16, 28, 98, and 152). Harris (1935) re­cords the species as very common in the zone of Diplograptus decoratus in the upper part of the Middle Ordovician of Victoria, Australia. Its associates in both the Marathon and Australian sequences include Cryptograptus schaferi, Trigono­graptus ensiformis, and lsograptus forcipi­formis . DIDYMOGRAPTUS NOVUS Berry, n. sp. Pl. 5, fig. 6, 7 Description.-The stipes are a maximum of 6 mm in length. They widen rapidly to a width of 0.4 mm and maintain that width throughout. The sicula is suspended from a fairly long nema (2 to 3 mm in length) and is about 0.8 mm in length. The stipes diverge from it at about a 180-degree angle and remain straight for the greater part of their length but curve slightly up­ward at their distal ends. The thecae num­ber 5 to 6 in 5 mm, are four times as long as they are wide, overlap one-half to two­thirds their length, and are inclined at an angle of 25 to 30 degrees to the stipe. The apertural margins are straight and are in­clined at an angle of 100 to 105 degrees to the stipe. This form resembles D. serpens (Monsen, 1937, p. 131) hut differs from it in the larger angle of divergence of the stipes, in the shorter length of the stipes, in the shorter sicula, and in the slightly higher angle of inclination of the thecae to the stipe. Horizon.-Specimens of this species were collected from the lower part of the Marathon limestone, zone 2 (collections 72C, 72D, and 72E). This is the earliest didymograptid to occur in the Marathon succession. Holotype.-Yale Peabody Museum No. 20254. Graptolite Faunas, Marathon Region DIDYMOGRAPTUS PACIFICUS Ruedemann Pl. 11, fig. 4 Didymograptus paci/icus Ruedemann, 1947, Geo!. Soc. America Mem. 19, pp. 340-341, pl. 54, figs. 30-32. Remarks.-The Texas specimens agree well with Ruedemann's specific descrip· ti on. Horizon.-Specimens of D. pacificus were collected from the lower part of the Fort Peiia formation, zone 8 (collections 107 and 140) . Ruedemann's types of the species came from the Sarback formation on Fossil Mountain 8.7 miles northeast of the Lake Louise Station on the Canadian Pacific Railway, Alberta, Canada. DIDYMOGRAPTUS PARAINDENTUS Berry, n. op. Pl. 11, figs. 1, 2 Description.-The stipes diverge from the sicula at an initial angle of 60 degrees then incurve and become subparallel. They widen rapidly to a maximum of 1 mm and maintain that width throughout and are a maximum of 1.2 cm in length. The sicula is 1.5 mm in length, 0.6 mm in width at its base, and tapers rapidly towards its apex. The thecae number 12 to 14 in 10 mm, are three times as long as they are wide, over­lap about one-half their length, and are inclined at a 25. to 30-degree angle to the stipe. The apertural margins are slightly concave and small mucros are present. This form resembles D. indentus but differs from it in having more closely set thecae and a much shorter sicula. Horizon.-Specimens of this species were collected from the lower part of the Fort Peiia formation, zone 8 (collections 61A and 141). Holotype.-Yale Peabody Museum No. 20253. DIDYMOGRAPTUS PATULUS (Hall) Pl. 6, fig. 9; Pl. 7, fig. S Graptolithus patulus Hall, 1858, Canada Geo!. Survey, Rept. Prog. for 1857, p. 131. Didvmograptus patulus Elles and Wood, 1901, Mon. British Grapt., pp. 13-14, text figs. Ba, b, pl. 1, figs. Ba·c. Didymograptus patulus Ruedemann, 1947, Geo!. Soc. America Mero. 19, pp. 341-342, pl. 55, figs. 17-22, pl. 56, figs. 16, 17. Remarks.-The Texas specimens agree fully with the description given by Ruede­mann. D. patulus is quite similar to D. ni­tidus, but the forms identified by the writer as D. patulus have wider and more rapidly widening branches and more inclined and curved thecae that are less closely arranged than in D. nitidus. Horizon.-D. patulus was first reported in the Marathon limestone by Ruedemann (in Sellards, 1933). The writer collected the species from zones 4, 5, and 6 of the upper part of the Marathon limestone, where it is abundant (collections 23, 25, 26, 32, 68, 69, 91, 102, and ll5). D. patulus is common in the horizons characterized by Tetragrapti and Didymo­grapti but does not persist to the zone of D. bifidus. In New York, Ruedemann re­cords the species as common in zone 1 (T etragraptus zone) of the Deepkill shale. Hall's type material came from the Levis shale in Quebec. Gurley (1896) lists it from the main Tetragraptus zone but Ray­mond (1914) did not mention it. D. patu­lus occurs in England in the middle and upper Arenig in Shropshire and in the lower Llanvirn of St. David's district in Wales associated with D. bifidus, D. artus, and D. nicholsoni. D. patulus ranges into a somewhat higher horizon in England than in Texas. DIDYMOGRAPTUS PROTOBIFIDUS Elles Pl. 8, figs. 5-9 Didymograptus protobifidus Elles, 1933, Geo!. Survey Great Britain, Summ. Prog. for 1932, p. 98, figs. 1-3. Didymograptus protobifidus Ripper, 1937, Royal Soc. Victoria, Proc. (n.s.), vol. 49, pp. 154--156, text fig. 1. Didymograptus protobifidus Ruedemann, 1947, Geo!. Soc. America Mem. 19, pp. 343-344, pl. 54, fig. 18. Remarks.-There appears to be con­siderable variation in the forms referred to D. protobifidus by various workers. However, the Texas specimens clearly fall within the range in variation in the species as delimited by Elles. The rhabdosomes of the Texas specimens are small. The stipes range from 1 to 2 cm in length and are 0.5 Bureau of Ecorwmic Geology, The University of Texas to 0.7 mm wide at their origin and increase to a maximum of 1.3 mm distally. They diverge initially at about 90 degrees but soon curve so that they become subparallel. The thecae number 12 to 14 in 10 mm, are free one-half their length, are inclined at a low, variable angle (20 to 45 degrees) to the axis of the stipe, and are slightly curved distally with apertural margins slightly oblique to the axis of the stipe. Horizon.-D. protobifidus is the most characteristic element of zone 6 in the upper part of the Marathon limestone and giYes its name to that zone. The species is very common in the zone (collections 23, 24F, 25, 30, 40, 40A, 52. 64, and ll5) and is confined to it. Ruedemann records the species from the West Spring Creek limestone of the Arbuckle group in the Arbuckle Mountains, Oklahoma, and from the limestone near Smithville, Ar­kansas. The writer has collected specimens of the species from the Deepkill shale in l\'ew York. D. protobifidus is found in the British Isles in the middle and upper parts of the Skiddaw slates in the zones of D. extensus and D. hirundo. In Australia, D. protobifidus is the characteristic element in the faunas of the lower two zones of the Chewton series of the Lower Ordovician. The species occurs in the British. Mara­thon, and Victorian sequences with ~xtensi­form Didymograpti, several species of T etragraptus including T etragraptus f ruti­cosus, and Phyllograpti. DIDY'.\IOGR . .\PTLS PROTOl:\"DE'iTt:S ~lonsen Didrmograptus protoindentus :'\fonsen, 1937, Norsk. Geo!. Tidsskr., Bd. 16. pp. 148-149, taf. 2, figs. 40, 4-0, 47, 54, taf. 5, fig. 1, taf. 10, figs. 16, 17. Remarks.-The Texas specimens agree closely with Monsen's specific description. Horizon.-Specimens of D. protoinden­ tus were collected from one locality only (collection 20), which is in zone 7. the highest beds of the Marathon limestone. Monsen's types came from the zone of Phyllograptus densus of the lower Didy­ mograptus shales in Norway. DIDYMOGRAPTUS SAGITTICAULIS Gorley Didymograptus sagitticaulis Gurley, 1896, four. Geo!., vol. 4, p. 68. Didymograptus sagitticaulis Ruedemann, 1908, New York State Mus. l\Iem. 11. pp. 248-251, text figs. 151-155, pl. 14. fig. 3. Didymograptus sagitticaulis Ruedemann, 1947, Geo!. Soc. America Mem. 19, pp. 344----345, pl. 55, figs. 3-5, pl. 56, figs. 12-14. Remarks.-The Texas specimens agree well with Ruedemann's specific description except that the thecae number 6 to 10 at the proximal end of the stipes, whereas the thecae number 7 in 10 mm in the same part of the stipe in the type material. Horizon.-D. sagitticaulis was collected from zone 12, the upper part of the Woods Hollow shale (collections 94A and 94C). The types of the species were collected from the l\ormanskill shale near Albany, New York, and the species has been re­ported in the Normanskill shale at several other localities. Ruedemann also reports the species from the Glenogle shale in British Columbia and the Womble shale in Arkansas. Decker (1952) lists it from sev­eral localities of the "Athens" shale in Virginia and Tennessee. DID'l:~OGRAPTL"S SERRATULUS (Hall) Graptolithus serratulus Hall, 1847, Paleontology of New York, ml. l, p. 274, pl. 74, figs. 5a-b. Did~mograptus serratulus Elles and Wood, 1901, :'\lon. British Grapt., pp. 29-30, text figs. 18a, b. pl. 2, figs. 7a, b. Didrmograpllls serratulus Ruedemann, 1947, Geo!. Soc. America Mem. 19, pp. 346-347, pl. 54, figs. 49-51. Remarks.-The Texas specimens are poorly preserved, but they appear to agree with the description given by Ruedemann. Horizon.-Specimens of D. serratulus were obtained from zones ll and 12, the upper part of the Woods Hollow shale (col­ lections 94A, 100, 104, 105, and 127). Ruedemann's types of this species came from the Normanskill shale at Kenwood, New York. The species has been recorded from other localities in the Normanskill shale and from the Stringtown shale in Oklahoma and the Womble shale in Ar­ kansas. Elles and Wood report the species in the Glenkiln shales of South Scotland Graptolite Faunas, Marathon Region and Etheridge (1878) listed the species in his catalogue of Australian fossils. DIDYMOGRAPTUS SIMILIS (Hall) Graptolithus similis Hall, 1865, Canadian Or­ganic Remains, p. 78, pl. 2, figs. 1-5. Didymograptus similis Ruedemann, 1947, Geol. Soc. America Mem. 19, p. 347, pl. 55, figs. 37­ 40. Remarks.-The Texas specimens agree fully with the description of this species by Ruedemann. Horizon.-D. similis was collected from zones 5, 6, and 7 of the upper part of the Marathon limestone (in collections 26, 47, 64, 67, and 70). Ruedemann states that this species is common in the zone of D. bi­fidus (graptolite beds 3 and 5) of the Deep­kill shale in New York. Raymond (1914) lists it in zone C-1 of the Levis shale in Quebec and Miser and Purdue (1929) list it from the Mazarn shale in the Ouachita Mountains. Harris and Thomas (1938b) figure D. similis as one of the characteris­tic species of the Bendigo series in Vic­toria, Australia. DIDYMOGRAPTUS SUBTENUIS (Hall) Graptolitus tenuis {Portlock?) Hall, 1847, Pale­ ontology of New York, vol. l, p. 272, pl. 74, figs. 2a-d. Didymograptus subtenuis Ruedemann, 1908, New York State Mus. Mem. 11, pp. 253-255, text figs. 160, 161, pl. 14, figs. 1, 2. Didymograptus subtenuis Ruedemann, 1947, Geo!. Soc. America Mem. 19, pp. 348-349, pl. 55, figs. 6, 7, pl. 56, figs. 5, 6. Remarks.-The Texas specimens agree well with Ruedemann's specific descrip· ti on. Horizon.-A few specimens of this spe· cies were collected from the lower part of the Woods Hollow shale, zone 11 ( collec­tion 137). The type specimens came from the Normanskill shale at Kenwood, New York. Other localities in the Normanskill shale have also yielded specimens of this species. Ruedemann records it in the Glen­ogle shale in British Columbia, and Decker (1952) found it in the "Athens shale" at localities in Tennessee. DIDYMOGRAPTUS V-DEFLEXUS Harri• Pl. 11, fig. 9 Didymograptus v-defiexus Harris, 1924, Royal Soc. Victoria, Proc. { n.s.), vol. 36, pp. 93-94, pl. 7, figs. 1, 2. Remarks.-The Texas specimens agree fully with the specific description by Har­ns. Horizon.-Specimens of this species were collected from only one locality (col­lection 141), which is the lower part of the Fort Pena formation, zone 8. Harris and Thomas (1938b) figure it as one of the characteristic species of the Y apeen series of Victoria, Australia, where it occurs with the same associates (Cardiograptus and Oncograptus) as it does in the Mara· thon region. Genus CARDIOGRAPTUS Harris and Keble, 1916 CARDIOGRAPTUS CRAWFORDI Harris Pl. 11, fig. 12 Cardiograptus crawfordi Harris, 1926, Royal Soc. Victoria, Proc. (n.s.), vol. 38, p. 57, pl. 1, figs. 5-7. Cardiograptus crawfordi Harris and Thomas, 1935. Royal Soc. Victoria, Proc. (n.s.), vol. 47, p. 306, fig. 2, no. 26. Remarks.-The Texas specimens are small, being 5 to 6 mm in length and 3.5 to 4 mm in width, but they agree in every respect with the description by Harris. Harris states that the usual dimensions are 7 mm in length and 5 mm in breadth but that "many specimens are smaller." Horizon.--C. crawfordi is a common ele­ment of the fauna of zone 8. It is found in the lower part of the Fort Pena formation at several localities (collections 42, 61A, 62, and 140). Harris (1935) lists the spe­cies from the zones of Diplograptus dec­oratus and Glyptograptus intersitus of the Victorian Middle Ordovician. C. craw­fordi occurs with C. morsus, Oncograptus, and I sograptus caduceus var. maxima in the Marathon sequence, but it occurs with T rigonograptus ensiformis, H allograptus etheridgei, and Cryptograptus schaferi in the Victorian succession. The species ap­pears earlier in the Marathon sequence than it does in the Australian. Bureau of Economic Geology, The University of Texas CARDIOGRAPTUS MORSUS Harris and Keble Pl. 11, figs. 13, 14 Cardiograptus morsus Harris and Keble, 1916, in Harris, 1916, Royal Soc. Victoria, Proc., vol. 29, pl. 1, figs. 1-4. Cardiograptus morsus Harris, 1924, Royal Soc. Victoria, Proc. ( n.s.), vol. 36, pp. 95-96. Remarks.-The Texas specimens agree closely with the specific description by Harris ( 1924) . Horizon.--C. morsus is a characteristic element of the fauna of zone 8 in the Mara­thon sequence. The species was found in the lower part of the Fort Pena formation (collections 42, 107, 140, and 141) where it occurs with Oncograptus upsilon and several varieties of I sograptus caduceus. Harris and Thomas (1938b) state that C. morsus is the characteristic species of the upper zone of the Y apeen series in Vic­toria, Australia. Genus ISOGRAPTUS Moberg, 1892 ISOGRAPTUS CADUCEUS var. DIVERGENS Harris Pl. 11, fig. 6 Isograptus caduceus var. divergens Harris, 1933, Royal Soc. Victoria, Proc. ( n.s.), vol. 46, p. 91, text figs. 14--18. Remarks.-The Texas specimens are like Harris' figures except that in most of the specimens, the stipes are inclined at a slightly larger angle than those figured by Harris. Some specimens show a distinct web structure at the axil much like Harris' text figure 17. Horizon.-Specimens of this variety were collected from both the lower part of the Fort Pena formation, zone 8 ( collec­tions 110 and 141), and the upper part of the formation, zone 9 (collection 15). Har­ris (1933) records the variety from beds now included in the upper zone of the Yapeen series in Victoria, Australia, where its associates include forms (Cardio­graptus and Trigonograptus) found in zone 8 in the Marathon sequence. Further, Harris ( 1935) lists the variety divergens from the lowest zone (zone of Glyptograp­tus a,ustrodentatus) of the Middle Ordo­vician in Victoria; its associates include several forms ( G. austrodentatus, I sograp· tus forcipiformis, and T etragraptus serra) found in zone 9 of the Marathon sequence. ISOGRAPTUS CADUCEUS var. IMITATA Harris lsograptus caduceus var. imitata Harris, 1933, Royal Soc. Victoria, Proc. ( n.s.), vol. 46, p. 92, text figs. 55-59. Remarks.-The Texas specimens are like Harris' text figures 55-58. Horizon.-Specimens of this variety were collected from the upper part of the Fort Pena formation, zone 9 (collections 42 and 152). Harris reports the variety to be common in the highest zone of the Cas­tlemaine series in Victoria, Australia. ISOGRAPTUS CADUCEUS var. LUNATA Harris lsograptus caduceus var. lunata Harris, 1933, Royal Soc. Victoria, Proc. (n.s.), vol. 46, p. 90, text figs. 3-6. Remarks.-The Texas specimens are like Harris' text figures 3 and 5. The stipes show only a slight variation in width (LO to 1.2 mm). Horizon.-Specimens of the variety were collected from the highest beds of the Marathon limestone, zone 7 (collection 70) , and from the Alsate shale (collections 18 and 113), which comprises the lower part of zone 8. In Victoria, Australia, ac­cording to Harris, the variety ranges from the upper part of the Chewton series, where it is rare, into the lowest part of the Castlemaine series, where it is the charac­teristic form of the lowest zone. Spjeldnaes (1953) has reported the form from the up­permost part of the lower Didymograptus shale, zone 3be exposed at Slemmested near Oslo, Norway. ISOGRAPTUS CADUCEUS var. MAXIMA Harris Pl. 11, fig. 8 lsograptus caduceus var. maxima Harris, 1933, Royal Soc. Victoria, Proc. ( n.s.), vol. 46, p. 91, text figs. 11 and 12. Remarks.-The Texas specimens are like Harris' figures except that in some specimens, the stipes enclose a lesser angle than the figured forms. Horizon.-Specimens of this variety were collected from the lower part of the Fort Pena formation, zone 8 (collections Grapwlite Faunas, Marathon Regi,on 61A, 88, 95, 107, 110, and 129). Harris records the variety from the middle and upper zones of the Castlemaine series in Victoria. Australia, and it is a character­istic form of the upper zone. It is associ­ated with /. caduceus var. vicwriae and /. caduceus var. maximo-divergens in the Australian sequence and is found in beds below those with Oncograptus and Cardio­graptus. In the Marathon succession, the varieties vicwriae, ma.xima, and maximo­divergens and Oncograptus and Cardio­graptus are all found together. ISOGRAPTUS CADUCEUS nr. MAXIMO-DIVERGENS Barris Pl. 11, fig. 11 lsograpt11s caduceus Yar. maximo-divergens Har­ ris. 1933. Royal Soc. Victoria, Proc. (n.s.) , rnl. 46, p. 91, fig. 13. lsograptus walcottnrum Ruedemann, 1947, Geol. Soc. America Mem. 19, p. 354, pl. 57, figs. 26-36. ~ Remarks.-The Texas specimens agree well with Harris' figure 13. The stipes of the Texas specimens measure 5 mm in width and enclose an angle of 45 to 55 de­grees between them. Ruedemann's figures of I. walcottorum also agree with Harris' figures of this variety of I. caduceus. Horizon.-Specimens of this variety were obtained from the lower part of the Fort Pena formation, zone 8 (collections 88 and 141 ), where they are associated with Oncograptus upsilon and /. caduceus var. vicwriae. Ruedemann's specimens came from the Glenogle shale in British Columbia. Harris records this variety from the highest zone of the Castlemaine -series, only, in Victoria, Australia, where it oc­curs in beds below those with 0. upsilon and above those with/. caduceus var. vic­wriae. ISOGRAP'nJS CADUCEUS Tar. VICTORIAE Barrie Pl. 11, fig. 7 lsograptu.s caduceus var. victoriae Harris, 1933, Royal Soc. Victoria, Proc. ( n.s.) , vol 46, p. 90, text figs. 7-10. Remarks.-The Texas specimens agree with Harris' figures. Horizon.-This variety is a common form in the lower part of the Fort Pefia formation, zone 8 (collections 10, 95, 98A, 110, 140, and 141). Harris states that the form is the diagnostic element of the mid­dle zone of the Castlemaine series in Vic­toria, Australia. In the Marathon region, the variety is associated with Cardiograp­tus, Oncograptus, and the more robust va­rieties of[. caduceus, while in Australia, it occurs in beds older than those containing Cardiograptus and Oncograptus. ISOGRAPTUS FORCIPIFORMIS var. LATUS Rnedemann PL 12, fig. l lsograptu.s /orcipi/ormis var. latus Ruedemann, 1947, Geo!. Soc. America Mera. 19, p. 353, pl. 57, figs. 41, 42. Remarks.-Ruedemann established this variety for fonns in which the width of the stipes remains constant for the greater part of their length. Otherwise, the variety a~rees with the typical form in all charac­ters. The Texas specimens agree well with Ruedemann's description of this variety ex­cept that the stipes are slightly narrower than the described material. The stipes of the Texas specimens are 2.5 to 2.8 mm irl width while Ruedemann gives a stipe width of 3.0 mm. Horizon.-Specimens of this variety were collected from the upper part of the Fort Pena formation, zone 9 (collections 15, 16, and 28 ). Ruedemann's type ma­terial came from the Blakely sandstone in Arkansas. Harris ( 1935) lists /. forcipi­formis from the lower three zones of the Middle Ordovician of the Victoria, Aus­tralia, sequence. ISOGRAPTUS MANUBRIATUS (T. S. Ball) Pl. 11, fig. 5; PL 12, fig. 4 Didymograptus caduceus var. manubriatus T. S. Hall, 1914, Royal Soc. Victoria, Proc. (n.s. ) • vol. 27, pp. 108-109, pl. 17, fig. 12 (not fig. 13). lsograptus manubriatus Harris, 1933, Royal Soc. Victoria, Proc. ( n.s.), vol. 46, pp. 102-104, pl. 6, figs. la·i. Remarks.-Harris (1933) fully dis­cusses the character of I. manubriatus, and the Texas specimens agree closely with his description. Bureau of Economic Geology, The University of Texas Horizon.-!. manubriatus was found in the lower and middle parts of the Fort Pena formation, zones 8 and 9 (collections 61A, 110, and 111). Harris records it from the Y apeen series of Victoria, Aus­tralia. It is associated with Oncograptus upsilon and lsograptus caduceus var. di­vergens in both the Marathon and Aus­tralian assemblages. ISOGRAPTUS OVATUS (T. S. Hall) Didymograptus ovatus T. S. Hall, 1902, Rec. Geol. Surv. Victoria, p. 33, fig. 1. Isograptus ovatus Harris, 1933, Royal Soc. Vic­toria, Proc. (n.s.), vol. 46, pp. 105-106, text figs. 45, 46. Remarks.-The Texas specimens agree well with the specific description by Harris. Horizon.-A few specimens of/. ovatus were collected from the upper part of the Fort Pena formation, zone 9 (collection 13). Harris records the species from the youngest zone of the Middle Ordovician in Victoria, Australia. Genus ONCOGRAPTUS T. S. Hall, 1914 ONCOGRAPTUS UPSILON T . S. Hall Pl. 11, figs. 10, 15 Oncograptus upsilon T. S. Hall, 1914, Royal Soc. Victoria, Proc. (n.s.), vol. 27, p. 109, pl. 17, fig. 14. Oncograptus upsilon Ruedemann, 1947, Geol. Soc. America Mem. 19, pp. 355-356, pl. 58, fig. 5. Remarks.-The Texas specimens agree closely with T. S. Hall's specific descrip­tion. Horizon.-Ruedemann (in Sellards, 1933) first reported 0. upsilon from the Marathon region, and the writer found it to be fairly common in the lower part of the Fort Pena formation, zone 8 ( collec­tions 61B, 107, 110, 140, and 141). Harris and Thomas ( l 938b) figure the species as a common form in the Ya peen series in Victoria, Australia, and state that it is the characteristic element of the lower zone of that series. ONCOGRAPTUS UPSILON var. BIANGULATUS (Harris and Keble) Oncograptus biangulatus Harris and Keble, 1916, in Harris, 1916, Royal Soc. Victoria, Proc., vol. 29, pl. 1, figs. 7-9. Oncograptus biangulatus Harris, 1924, Royal Soc. Victoria, Proc. ( n.s.), vol. 36, p. 96. Oncograptus upsilon var. biangulatus Harris, 1933, Royal Soc. Victoria, Proc. (n.s.), vol. 46, p. 96, text figs. 23, 24. Remarks.-The Texas specimens agree with Harris' ( 1933) text figure 23 and. with his discussion of the variety. Horizon.-Specimens of this variety were collected from the lower part of the Fort Pena formation, zone 8 (collections 140 and 141) . Harris records the variety from both zones in the Ya peen series in Victoria, Australia. The species has the same associates (Cardiograptus, 0. upsilon, and Didymograptus v-deflexus) in both the Victorian and Marathon sequences. Family CORYNOIDIDAE Bulman, 1944 Genus CORYNOIDES Nicholson, 1867 CORYNOIDES CALICULARIS Nicholson PI. 15, fig. 5 Corynoides calicularis Nicholson, 1867, Geol. Mag., vol. 4, p. 108, pl. 7, figs. 9-11. Corynoides gracilis Ruedemann, 1947, Geol. Soc. America Mem. 19, p. 361, pl. 58, figs. 34-37a. Corynoides gracilis mut. perungulatus Ruede­ mann, 1947, Geol. Soc. America Mem. 19, p. 361, pl. 58, figs. 38-46. Corynoides calicularis Strachan, 1949, Geol. Mag., vol. 86, pp. 156-157, text fig. 1. Not. Corynoides calicularis Ruedemann, 1908, New York State Mus. Mem. 11, p. 234, text figs. 126-131, pl. 13, figs. 1, 6-8. Remarks.-ln his revision of the genus Corynoides, Strachan (1949) has brought up to date the synonymy of this species and a part of it is given above. The Texas speci­mens agree with Ruedemann's description of C. gracilis mut. perungulatus. Strachan states that the American forms C. gracilis and C. gracilis mut. perungulatus agree well with what is accepted as C. calicularis in Britain, and the writer, following this opinion, includes the Texas forms in the species C. calicularis. H orizon.--C. calicularis is a relatively common form in zones 11 (collections 104, 122, 125, and 139) and 12 (collections 94A and 136) in the Woods Hollow shale. Ruedemann records C. gracilis mut. perun­gulatus as abundant in the Normanskill shale in New York, the Womble shale in Arkansas, and the Stringtown shale in Graptolite Faunas, Marathon Regwn Oklahoma. He also reports C. gracilis from the Normanskill and Snake Hill shales in New York and the Stringtown shale in Oklahoma. Strachan states that C. calicu­1.aris is common in the zone of Climaco­graptus wilsoni and also found in the suc­ceeding zone-that of DU:ranograptus clin­gani in the British Isles. The American oc­currences of C. calU:ularis are slightly ear­lier than those in the British Isles. CORYNOIDES INCURVUS Haddlng Corynoides incun·us Radding, 1915, Lunds. Univ. Arsskr., N.F., Afd. 2, Bd. 11, p. 25, pl. 3, figs. 24-27. CorYnoides calicularis Ruedemann. 1908, New York State Mus. Mem. 11, p. 234, text figs. 126-131, pl. 13. figs. 1, 6-8. Corynoides curtus mut. pristinus Ruedemann, 1947. Geol. Soc. America Mem. 19, p. 360, pl. 58, fie:s. 30-33. Corrnoides incurvus Strachan, 1949, Geol. Mag., vol. 86, pp. 158-159, text fig. 3. Remarks.-The Texas specimens were compared to material identified as C. cur· tus mut. pristinus by Ruedemann and were considered to be identical to it. Fur­ ther, the measurements of specimens of this species agree with the description given by Strachan for the species C. in­ curvus. Following Strachan's suggestion, the writer includes the Texas specimens and Ruedemann's form C. curtus mut. pristinus in the species C. incurvus. Horizon.-Only a few specimens of this species were found in Texas. They were collected from the Woods Hollow shale, zones 11 (collection 104) and 12 ( collec­tion 105). Ruedemann records C. curtus mut. pristinus from the Normanskill shale in New York and from low in the Viola limestone in Oklahoma. Strachan reports C. incurvus from the Hartfell shales in the zone of DU:ranograptus clingani. The American representatives of this species appear slightly earlier than do the English forms. CORYNOIDES TRICOR.1\llS Raedemann Corynoides tricornis Ruedemann, 1947, Geo!. Soc. America Mem. 19, p. 362, pl. 58, figs. 61­ 64. Remarks.-The Texas specimens agree well with Ruedemann's specific descrip· tion. The characteristic element of this spe­cies is the needlelike apertural spine with which each theca is provided. The rhab· dosome is easily recognized by its short (4 mm), narrow (0.3 to 0.5 mm) size and the apertural spines. Horizon.-Specimens of C. tricornis were collected from the lower and middle parts of the Woods Hollow shale, zones 11 (collection 137) and 12 (collection 103). Ruedemann's type material came from the lower part of the "Athens" shale near Bristol, Tennessee. He also reports it in the Glenogle shale in British Columbia. Family CRYPTOGRAPTIDAE Radding, 1915 Genus CRYPTOGRAPTUS Lapworth, 1880 CRYPTOGRAPTUS SCHAFERI (Lapworth) Pl. 12, figs. 7, 8 Cryptograptus tricornis var. schaferi Lapworth, 1880, Ann. Mag. Nat. Hist., vol. 5, pl. 5, figs. 28a, b. Cryptograptus tricornis var. schaferi Elles and Wood, 1908, Mon. British Grapt., p. 299, text figs. 20la, b, pl. 32, figs. 13a-c. Cryptograptus schaferi Bulman, 1933, Quart. Jour. Geol. Soc. London, vol. 89, pp. 352-353. Cryptograptus schaferi Harris and Thomas, 1935, Royal Soc. Victoria, Proc. (n.s.), vol. 47, p. 304, fig. 3, nos. 11, 12. Remarks.-Bulman raised Lapworth's variety schaferi of C. trU:ornis to specific rank, and the writer follows this opinion. C. sclwferi is 2.0 mm in width, whereas C. tricomis is 1.5 mm in width, and the short free edges of the thecae in C. sclwf eri give rise to distinct mucronate extensions. Further, there are no conspicuous basal spines in C. schaferi whereas in C. tri­comis such spines are prominent. The rhabdosomes of the Texas specimens are 15 to 20 mm in length, parallel sided, and have a breadth of about 2.0 mm. The thecae number 11 to 12 in 10 mm and have conspicuous mucronate extensions. The initial two thecae appear to have grown downward before upward growth commenced. Horizon.-The species is common in the upper part of the Fort Pena formation, zone 9 (collections 13, 14, 15, 28, and 98). Elles and Wood record the species from a Bureau of Economic Geology, The University of Texas younger horizon, the zone of N emagraptus gracilis, in the Glenkiln shales in the British Isles. Harris and Thomas (1938) state that it is common in the middle two zones (zones of Glyptograptus intersitus and Diplograptus decoratus) of the Middle Ordovician of Victoria, Australia. The Texas specimens occur with similar as­semblages to those with which the species occurs in Australia. Probably all of the Middle Ordovician forms referred to C. tricornis by the several Australian authors should be referred to C. schaferi; there­fore, C. tricornis would not have as long a range in Australia as would appear from the literature. CRYPTOGRAPTUS TRICORNIS (Carruthers) Pl. 15, fig. 9 Diplograpsus tricornis Carruthers, 1858, Royal Phys. Soc. Edinburgh, Trans., vol. 1, p. 468, fig. 2. Cr:vptograptus tricornis Elles and Wood, 1908, Mon. British Grapt., pp. 296-298, text figs. 200a-j, pl. 32, figs. 12a-d. Cryptograptus tricornis Ruedemann, 1947, Geo!. Soc. America Mem. 19, p. 446, pl. 76, figs. 23­ 33. Cryptograptus tricornis mut. insecti/ormis Ruede­mann, 1947, Geol. Soc. America Mem. 19, pp. 446-447, pl. 76, figs. 34-41. Remarks.-The Texas specimens agree closely with the specific description by Elles and Wood. Bulman (personal corn· munication, September 1956) states that he considers C. tricornis mut. insectiformis to be merely an immature scalariform view of C. tricornis, and the writer concurs with this opinion. Horizon.--C. tricornis is common in the Woods Hollow shale where it was collected from both zones 11 (collections 49, 104, 122, 125, 137, 139, and 150) and 12 (col­lections 94A, 94B, 100, 103, 105, and 136). Ruedemann reports C. tricornis as com­mon in the Normanskill shale in New York, and that it is known from the Magog shale in Quebec, the Womble shale in Arkansas, the Stringtown shale and Viola limestone in Oklahoma, and the Glenogle shale in British Columbia. Further, he records C. tricornis mut. insectiformis from the Snake Hill shale in New York and from the Viola limestone. In the British Isles, C. tricornis is a long-ranging species. Elles and Wood state that it is abundant in the zones of Didymograptus murchisoni, Nemagraptus gracilis, Climacograptus peltifer, and Cli­macograptus wilsoni, and that it is also found in the zones of Didymograptus ex­tensus, Didymograptus bifidus, and Di­cranograptus clingani. Thomas and Keble (1933) record C. tricornis from the Gis­bornian and Eastonian series of the Upper Ordovician in Victoria, Australia. Genus GLOSSOGRAPTUS Emmons, 1855 GLOSSOGRAPTUS ACANTHUS Elles and Wood Glossograptus acanthus Elles and Wood, 1908, Mon. British Grapt., p. 314, text figs. 208a, b, pl. 33, figs. 4a-c. Glossograptus acanthus Harris and Thomas, 1935, Royal Soc. Victoria, Proc. (n.s.), vol. 47, pp. 302-303, fig. 3, nos. 13-16. Remarks.-The Texas specimens agree well with Elles and Wood's specific descrip­tion except that no septal spines were ob­served. However, Elles and Wood were not certain that septal spines were present. The preservation of the Texas specimens is such that it is difficult to see both of the apertural spines belonging to each theca (Elles and Wood also mention that more than one of the two apertural spines is rarely seen), but the two spines appear to be preserved one almost on top of the other, so that the process which extends out from the aperture of each theca appears thicker than it really is. G. acanthus is readily recognized by its subfusiform outline, its breadth (up to 4 mm), and its robust spines. Horizon.-Specimens of G. acanthus were collected from the upper part of the Fort Pena formation, in zone 9 (collections 13, 14, and 149), where it occurs with Hallograptus etheridgei, Trigonograptus ensiformis, and Glosso.graptus hincksii. Elles and Wood report that G. acanthus oc­curs in the zones of Didymograptus bifidus and D. extensus of the Arenig, Skiddaw slates in England. Harris and Thomas (1935) state that G. acanthus is common in the Middle Ordovician (zone of Glypto­ Grapwlite Faunas, graptus intersitus) of Victoria, Australia. It occurs there in an assemblage quite like that with which it occurs in Texas. It oc­curs in an older horizon in England than it does in Texas and Australia. GLOSSOGRAPTUS ARMATUS Nieholson Glossograptus armatus Nicholson. 1869, Ann. Mag. Nat. Hist .. vol. 4. p. 234, pl. 11, fig. 8. Glossograptus armatus Elles and Wood, 1908, Mon. British GrapL, pp. 312-313, text fig. 207, pl. 33. figs. 5a-e. Remarks.-The Texas specimens agree fully with the specific description by Elles and Wood. Hori::.on.-A few specimens of G. arma­tus were collected from one locality (col­lection 137) which is in the lower part of the Woods Hollow shale, zone 11. Elles and Wood report that the species is a rare fossil in the upper part of the Skiddaw slates and in the Glenkiln shale in the British Isles. GLOSSOGRAPTUS CILIATUS Emmons? Remarks.-All the Texas specimens are small and are probably young forms. They are like Ruedemann's (1947) figures of tht> early stages of G. cih~atus (pl. 77, figs. 28­31) and have. therefore, been referred to that species. No adult specimens were found. Hori::.on.-The ~pecimens referred to G. ciliatus were collected from both zones 11 (collections 104 and 139) and 12 (collec­tions 94A. 127. and 136) in the Woods Hollow shale. Ruedemann records G. cili­atus from the \"ormanskill shale in New York, the Womble shale in Arkansas. and the Viola limestone in Oklahoma. GLOSSOGRAPTliS Hl:'l"CKSII (Hopkinson) Pl. 12, fig. 9a Diplograptus hincksii Hopkinson, 1Bi2, Geo!. \fag.. \"Oi. 9. p. 507, pl. 12, fig. 9. Glo;sograptus hincksii Elles and Wood. 1908. \ion. British Grapt.. pp. 309-312, text figs. 205 a-L pl. 33, figs. 2 a-j. Renia.rks.-The Texas specimens agree well with the specific description by Elles and Wood. Hori::.on.--G. hincksii is a characteristic species of zone 9 I, collections 13, 28, and Marathon Regwn 71 149), which encompasses the upper part of the Fort Pefia formation. It was also collected from the lower part of the Woods Hollow shale (collection 137) which is in zone 11. Elles and Wood report the species to be present in the zones of N emagraptus gracilis, Mesograptus multidens, and Cli­macograptus wilsoni in the British suc­cession. Harris (1935) lists G. hincksii as a common fossil in the upper two zones of the Middle Ordovician and Thomas and Keble (1933) list it from the Gisbornian series of the Upper Ordovician in Victoria, Australia. The species occurs earlier and does not range as high in the Marathon and Victorian successions as it does in the British. GLOSSOGRAPTUS HORRIDUS Ruedemann Glossogra.ptus ciliatus mut. horridus Ruedemann, 1908. New York State J\Ius. l\Iem. 11, pp. 383­ 384, pl. 26, figs. 8, 9, pl. 27, fig. 5. Glossograptus horridus Ruedemann, 1947, Geo!. Soc. America Mem. 19, pp. 451-452, pl. 7i, figs. 17-22. Remarks.-The Texas specimens agree fully with Ruedemann's specific descrip­ tion. Horizon.-Specimens of G. horrUlus were collected from one locality (collection 28) which is in the upper part of the Fort Pena formation, zone 9. Ruedemann re­ ports the species in shales from Summit, Nevada. and from the Glenogle shale in British Columbia. GLOSSOGRAPTUS HYSTRIX Ruedemann Glossograptus hystrix Ruedemann, 1904, New York State Mus. Mem. 7, pp. 724-725, text fig. IOL pl. 16, figs. 27-29. Glossograptus hystrix Ruedemann, 1947, Geo!. Soc. America Mem. 19, p. 452, pl. 77, figs. 1-4, not figs. 5-8. Remarks.-The Texas specimens agree fully with Ruedemann's specific descrip­tion and with the figures of the New York specimens. The figured forms from Arkan­sas are narrower and possess a distinct vir­gula. They appear to be a species distinct from G. hystrix. Horizon.-Specimens of G_ hystrix were collected from the upper part of the Fort Pena formation, zone 9 (collections 15 Bureau of Ecorwmic Geology, The University of Texas and 98) . Ruedemann records the species from graptolite bed 7 (zone of Diplograp· tus dentatus) of the Deepkill shale in New York, and from the Ash Hill quarry at Mt. Merino, New York. Family LEPTOGRAPTIDAE Lapworth, 1879 Genus LEPTOGRAPTUS Lapworth, 1873 LEPTOGRAPTUS ANNECTANS (Walcott) Graptolithus annectans Walcott, 1881, Albany Inst. Trans., vol. 10 (Adv. sheet 1879), pp. 20, 35, pl. l, fig. 2, 2a. Leptograptus annectans, Lapworth, 1887, Royal Soc. Canada, Proc. Trans., vol. 4, p. 183. Leptograptus annectans Ruedemann, 1947, Geo!. Soc. America Mem. 19, pp. 362-363, pl. 59, figs. 1-6. Remarks.-The Texas specimens are poorly preserved, but the measurements agree with the description of L. annectans by Ruedemann. The stipes are long ( 4 cm) and thin (0.4 mm increasing to 0.8 mm) and show a gentle double curvature. They diverge at a 290-degree angle. The thecae number 10 in 10 mm, overlap half their length, and are inclined at 15 degrees. H orizon.-Specimens of L. annectans were collected from one locality (collection 83A) in the middle part of the Maravillas chert, which is within zone 14. Walcott's type came from the Utica shale at Holland Patent, New York. Ruedemann records the species from the Fulton shale at Cincinnati and from the Viola limestone in the Ar­buckle Mountains, Oklahoma. LEPTOGRAPTUS FLACCIDUS mut. TRENTONENSIS Ruedemann Pl. 15, fig. 7 Leptograptus /laccidus mut. trentonensis Ruede­ mann, 1908, New York State Mus. Mem. 11, pp. 261-262, text. figs. 172-175, pl. 14, figs. 6, 7. Leptograptus fla ccidus mut. trentonensis Ruede­ mann, 1947, Geo!. Soc. America Mem. 19, pp. 366-367, pl. 59, figs. 14--17. Remarks.-The Texas specimens agree closely with Ruedemann's description, ex­cept that the angle of divergence of the stipes is 240 to 260 degrees in the Texas specimens while in the types it is 220 to 240 degrees. In one of the Texas specimens the sicula measures 2.0 mm in length. The usual length is 1.5 mm, according to Ruede­mann's description. Horizon.-This species was collected from zone 11, the lower part of the Woods Hollow shale (collections 49, 125, and 139). Ruedemann's types came from the N ormanskill shale in New York, and he has recorded it from the base of the Viola limestone in Oklahoma. LEPTOGRAPTUS VALIDUS var. INCISUS Lapworth! Remarks.-The Texas specimens tenta­tively referred to this variety are poorly preserved and details are difficult to see. They have long slender stipes which are about 0.4 mm in width. The thecae num­ber 8 to 10 in 10 mm, overlap about one· third of their extent, and are inclined at an angle of 15 degrees to the stipe. In these characters, the Texas specimens agree with the description of L. vmidus var. incisus, but the preservation of the sicular region and the detail -of the thecae is too poor to warrant definite identification. Horizon.-These forms were collected from zones 11 (collections 104 and 139) and 12 {collection 94A) in the Woods Hollow shale. L. vmidus var. incisus is re­corded from the Glenkiln shales of south­ern Scotland by Elles and Wood (1903, p. 115). Genus NEMAGRAPTUS Emmons, 1855 NEMAGRAPTUS EXILIS var. LINEARIS Ruedemann Nemagraptus exilis var. linearis Ruedemann, 1908, New York State Mus. Mem. 11, pp. 290-­ 291, text figs. 204, 205, pl. 17, figs. 10--12. Nemagraptus exilis var. linearis Ruedemann, 1947, Geo!. Soc. America Mem. 19, p. 372, pl. 61, figs. 10--14. Remarks.-The Texas specimens of this variety are poorly preserved but agree with Ruedernann's description. The exceeding slenderness and the restriction of the sec­ondary stipes to a small number at the distal ends of the main stipes distinguish this variety from the true N. exilis. Horizon.-This variety was found in the lower part of the Woods Hollow shale, zones 11 and 12 (collections 104, 136, 137, 139, and 148). Ruedemann reports the variety to be present in the Normanskill Graptolite Faunas, Marathon Region shale in New York, the Glenogle shale in British Columbia, and the "Athens" shale near Bristol, Tennessee. NEMAGRAPTUS GRACIUS (Dall) Pl. 15, fig. 13 Graptolithus gracilis Hall, 1847, Paleontology of New York, vol. 1, p. 274, pl. 74, figs. 6a·d. Nemagraptus gracilis Elles and Wood, 1903, Mon. British Grapt., pp. 127-129, text figs. 76a· c, pl. 19, figs. la-£. Nemagraptus gracilis Ruedemann, 1947, Geol. Soc. America Mem. 19, pp. 367-368, pl. 60, figs. 1-12. Remarks.-The Texas specimens agree well with the specific description by Elles and Wood and by Ruedemann. Horizon.-N. gracilis was found in zone 11 (collections 122 and 139), in the lower part of the Woods Hollow shale. The species is the most typical, but not the most com­mon, form of this zone. Hall described the species from the Normanskill shale in New York, and it has since been reported from Newfoundland, Maine, New Jersey, Vir­ginia, Alabama, and Arkansas (Ruede­mann, 1947) . Elles and Wood record it as one of the commonest elements of the graptolite fauna of the Glenkiln shales, and Harris and Thomas (1938b) list it as one of the characteristic species of the lower part of the Gisbornian series in the Upper Ordovician of Victoria, Australia. NEMAGRAPTUS GRACIUS nr, SURCULARIS (Hall) Graptolithus gracilis Hall, 1860, (pars) New York State Cab. Nat. Hist., 13th Ann. Rept., p. 56. figs. 1-4. Coenograptus surcularis Hall, 1868, New York State Cab. Nat. Hist., 20th Ann. Rept., p. 179, figs. 13-16. Nemagraptus gracilis rnr. surcularis Elles and Wood. 1903, Mon . British Grapt., pp. 129-130, text figs. iia-c. pl. 19, figs. 2a-d. Nemagraptus gracilis var. surcularis Ruedemann, 1947. Geo!. Soc. America Mem. 19, p. 370, pl. 60, figs. 17-24. Remarks.-The Texas specimens agree well with Elles and Wood's description. Horizon.-This variety of N. gracilis was found associated with the typical form in zone 11 (collection 137), the lower part of the Woods Hollow shale. Ruedemann re­cords the variety from the Normanskill shale of New York and the Stringtown shale of Oklahoma. Elles and Wood state that the variety is a "comparatively com· mon form in the Glenkiln shales of South Scotland." Family DICRANOGRAPTIDAE Lapworth, 1873 Genus DICELLOGRAPTUS Hopkinson, 1871 DICELLOGRAPTUS COMPLANATUS Lapworth Pl. 20, fig. 1 Dicellograptus complanatus Lapworth, 1880, Ann. Mag. Nat. Hist., vol. 5, p. 160, pl. 5, figs. 17a-e. Dicellograptus complanatus Elles and Wood, 1904, Mon. British Grapt., pp. 139-140, text figs. 84a-e, pl. 20, figs. la-d. Dicellograptus complanatus Ruedemann, 1947, Geol. Soc. America Mem. 19, pp. 376-377, pl. 62, figs. 4-10. Remarks.-The Texas specimens agree with the description by Elles and Wood in the character of the thecae, in number of thecae (8 to 10 in 10 mm), in the width of the stipes, and in the angle of divergence of the stipes (240 to 270 degrees). The stipes are shorter than those described by Elles and Wood. Horizon.-D. complanatus was obtained from collections made 8 inches and 1 inch from the top of the Maravillas chert, zone 15 (collections 60 and 147). The species was originally described from the upper part of the Hartfell shales of southern Scot­land. Ruedemann (1947) records it from the Sylvan shale in the Arbuckle Moun­tains, Oklahoma, and from the Polk Creek shale in the Ouachita Mountains in Arkan­sas. Harris and Thomas ( 1938b) report a DU:ellograptus cf. complanatus from the highest beds of the Bolindian series of the Upper Ordovician in Victoria, Australia. DICELLOGRAPTUS COMPLANATUS var. ARKANSASENSIS Ruedemann Pl. 20, fig. 2 Dicellograptus complanatus var. arkansasensis Ruedemann, 1947, Geo!. Soc. America Mem. 19, p. 377, pl. 62, figs. 11-15. Remarks.-The Texas specimens agree closely with Ruedemann's description. This variety is similar to the variety ornatus but lacks the stout lateral spines so character­istic of that form. Horizon.-This variety of D. complana­ tus was found associated with the typical Bureau of Economic Geology, The University of Texas form and the variety ornatus in the top of the Mara villas chert, zone 15 (collections 60 and 147). Ruedemann (1947) de­scribed the variety from the Polk Creek shale in Arkansas. DICELLOGRAPTUS COMPLANATUS var. ORNATUS Elles and Wood Pl. 20, fig. 3 Dicellograptus complanatus var. omatus Elles and Wood, 1904, Mon. British Grapt., pp. 14(}-141, text figs. 85a, b, pl. 20, figs. 2a-c. Dicellograptus complanatus var. omatus Ruede­mann, 1947, Geo!. Soc. America Mem. 19, pp. 377-378, pl. 62, figs. 16-20. Remarks.-The Texas specimens not only possess the characteristic stout lateral spines of the variety but also agree closely with the description given by Elles and Wood in all other characters. Horizon.-This variety of D. complana­tus was found in association with D. com­planatus and D. complanatus var. ar­kansasensis in the uppermost foot of the Maravillas chert, zone 15 (collection 60). The variety was originally described from the upper part of the Hartfell shales (the zone of Dicellograptus anctps) in southern Scotland. It has been recorded by T. S. Hall (1920) from New South Wales and by Thomas and Keble ( 1933) from the Bo­lindian series of the Upper Ordovician of Victoria, Australia. Ruedemann (1947) reported the species from the Ordovician shale of Trail Creek, Blaine County, Idaho. DICELLOGRAPTUS DIVARICATUS (Hall) Pl. 15, fig. 12 Graptolithus divaricatus Hall, 1859, Paleontology of New York, vol. 3, pp. 513-514, figs. 1-4. Dicellograptus divaricatus Elles and Wood, 1904, Mon. British Grapt., pp. 14~144, text figs. 87a-c, pl. 20, figs. 5 a, b. Dicellograptus divaricatus Ruedemann, 1947, Geo!. Soc. America Mem. 19, pp. 378-379, pl. 62, figs. 22-25. Remarks.-The Texas specimens agree well with the specific description by Ruede­mann. Horizon.-D. divaricatus was found in the Woods Hollow shale, zones 11 and 12 (collections 104, 122, 127, 136, and 139). The species was originally described from the Normanskill shale in New York, and it has been reported in the Womble and Stringtown shales in Arkansas and Oklahoma by Ruedemann. In the Brit­ish Isles, the species is recorded from the Glenkiln shale by Elles and Wood. Harris and Thomas ( 1938b) state that the species is characteristic of the Gisbornian series of the Upper Ordovician of Victoria, Aus­tralia. DICELLOGRAPTUS DIVARICATUS var. SALOPIENSIS Elles and Wood PL 16, fig. 1 Dicellograptus divaricatus var. salopiensis Elles and Wood, 1904, Mon. British Grapt., pp. 145­ 146, text figs. 89a, b, pl. 20, figs. 7a-e. Dicellograptus divaricatus var. salopiensis Ruede­ mann, 1947, Geo!. Soc. America Mem. 19, p. 380, pl. 63, figs. 2-3. Remarks.-The Texas specimens are poorly preserved, but the stipes maintain a uniform width of 15 mm throughout their length and the thecae are of the same type as D. divaricatus. Elles and Wood give these characteristics as diagnostic of this variety. Horizon.-The variety was found in zone 12 (collections 127 and 136) in the upper part of the Woods Hollow shale. Ruedemann reports it in the Normanskill shale of New York and the Stringtown shale of Oklahoma, and Elles and Wood report it in the Glenkiln shale of southern Scotland. Thomas and Keble (1933) list it from the Gisbornian series of the Aus­tralian Upper Ordovician. DICELLOGRAPTUS FORCHAMMERI (Gelnltz)? Remarks.-Some poorly preserved speci­mens of a Dicellograptus are questionably referred to this species. The stipes are about 1 to 1.2 mm in breadth, and the the­cae are the same number (8 to 10 in 10 mm) and have the same characteristics as given in the description of D. forchammeri by Elles and Wood ( 1904, Mon. British Grapt., pp. 150-152, text figs. 94a-d, pl. 22, figs. la-d). However, no detail of the proximal end can be seen and specific identification is not warranted. Horizon.-The specimens tentatively re­ Grapwlite Faunas, Marathon Region £erred to D. forchammeri were found in the middle part of the Maravillas chert, zone 14 (collections 83B and 93) . Accord­ing to Elles and Wood (1904) , D. forcham­meri is common in the British Isles in the zone of Dicranograptus clingani of the Hartfell shales, but it ranges from the zone of Nema.graptus gracilis in the Glenkiln shales to the zone of Pleurograptus linearis in the upper part of the Hartfell shales. The species is listed from the Viola lime­stone in Oklahoma \Ruedemann) and from the lower part of the Bolindian series in the Australian Upper Ordovician by Thomas and Keble (1933). DICELLOGRAPTUS FORCHAMMERI var. FLEXUOSUS Lapwortb Pl. 19, fig. 1 Dicellograptus .forchammeri rnr. flexuosus Lap­worth, 1876, Cat. West. Scottish Foss., pl. 4, fig. 90. Dicellograptu.s /orchammeri rnr. flexuosus Elles and Wood. 1904. l\lon. British Grapt., pp. 152­ 153. text figs. 95a-d. pl. 22. figs. 2a-d. Dicellograptus forchammeri Ruedemann, 1947, Geo!. Soc. America Mem. 19, p. 382, pl. 63, figs. 13-20. Remarks.-The Texas specimens agree in the character and number of thecae (IO to 8 in IO mm) with the description of this nriety given by Elles and Wood, but the width of the stipes is slightly less (0.4 mm at their origin and 0.8 mm distally). The Texas forms are immature, however, and the longest stipes measure but 5 cm in length while stipe lengths up to 14 cm were recorded by Elles and Wood. Hori.zon.-The specimens of D. for­ chammeri var. flexuosus were collected from the lower part of the Maravillas chert, zone 13 (collections 134 and 134A). The variety is found in the Hartfell shales (zones of Climacograptus wilsoni and Dicranograptus clingani) of southern Scot­ land. The variety occurs in the Viola lime­ stone and the Polk Creek shale of Arkansas. Thomas (1932) included D. forchammeri var. flexuosus in a list of graptolites from Upper Ordovician localities in Australia. DICELLOGRAPTUS GURLEYI Lapworth PL 16, fig. 9 Dicellograptus gurleyi Lapworth MS, 1890. Dicellograptus gurleyi Gurley, 1896, Jour. Geo!., \'OJ. 4, pp. 70--71. Dicellograptus gurleyi Ruedemann, 1908, New York State Mus. Mera. 11, pp. 303-306, text figs. 223-228, pl. 19, figs. 7-10. Dicellograptus gurleri Ruedemann, 1947, Geol. Soc. America Mem. 19, pp. 382-383, pl. 63, figs. 21-33. Remarks.-The Texas specimens are all immature forms, but in the character and number of thecae and in the character of the proximal end they agree with the de­scription by Ruedemann. Horizon.-D. gurleyi was found in zones 11 and 12 (collections 122, 136, 137, and 139) in the Woods Hollow shale. The type material came from the Normanskill shale at Stockport, New York, and Ruedemann found the species in collections from other localities m the Normanskill shale. Decker's (1952) collections from the Womble shale of Arkansas included this species. Teale (1919) listedD.gurleyifrom the Upper Ordovician of Victoria, Aus­tralia. DICELLOGRAPTUS GURLEYI var. EXILIS Ruedemann Dicel!ogra;Jtns gur/eYi rnr. exilis Ruedemann, 19-H. Geo!. Soc. America Mem. 19, p. 383, pl. 63, figs. 34-36. Remarks.-The stipes of the Texas speci­mens are slightly more slender ( 0.2 to 0.3 mm in breadth) than Ruedemann's de­scription, but the specimens agree in all other features. llorizon.-The variety was collected from zone 1 L the lower part of the Woods Hollow shale (collection 137). Ruedemann described the variety from material col­lected from the "Athens shale" at Pratts Ferry, Alabama. DICELLOGRAPTUS INTORTUS Lapworth PL 15, fig. 1 Dicellograptu.s intortus Lapworth, 1880, Ann. l\fag. Nat. Hist., vol. 5, p. 161, pl. 5, fig. 19a. Dicellograptus intortus Elles and Wood, 1904, Mon. British Grapt., pp. 146-147, text figs. 90a-d, pl. 20, figs. 4a-f. Dicellograptus intortu.s Ruedemann, 1947, Geo!. Soc. America Mem. 19, pp. 383-384, pl. 64, figs. 1-3. 7'6 Bureau of Economic Geology, The University of Texas Remarks.-The Texas specimens agree well with the specific description given by Elles and Wood. Horizon.-This species was found in zones 11and12 in the Woods Hollow shale (collections 104, 122, 136, 139, 148, and 150) . Elles and Wood record it from the Glenkiln shales in South Scotland. Ruede­mann reports it from the Normanskill shale in New York and the Womble shale in Arkansas. Harris and Thomas (l 938b) figure D. intortus with the characteristic forms of the Gisbornian series of the Upper Ordovician of Victoria, Australia. DICELLOGRAPTUS MOFFATENSIS var. ALABAMENSIS Ruedemann PL 15, fig. 10 Dicellograptus moffatensis var. alabamensis Ruedemann, 1908, New York State Mus. Mem. 11, pp. 310-312, text figs. 234-236, pl. 20, figs. 1, 2. Dicellograptus moffatensis var. alabamensis Ruedemann, 1947, Geol. Soc. America Mem. 19, p. 385, pl. 64, figs. 12-16. Remarks.-The Texas specimens agree with the description of this variety given by Ruedemann, except that the web between the stipes at the proximal end is very slight, whereas in the type material it is more prominent. Horizon.-0. mo.ffatensis var. alabam­ensis was collected from zone 11, the lower part of the Woods Hollow shale ( collec­tions 139 and 150) . Ruedemann described the variety from the "Athens shale" at Pratts Ferry, Alabama. DICELLOGRAPTUS PATULOSUS Lapworth Dicellograptus patulosus Lapworth, 1880, Ann. Mag. Nat. Hist., vol. 5, p. 162, pl. 5, figs. 18a-f. Dicellograptus patulosus Elles and Wood, 1904, Mon. British Grapt., pp. 147-148, text figs. 9la-e, pl. 21, figs. 5a-e. Dicellograptus patulosus Ruedemann, 1947, Geo!. Soc. America Mem. 19, p. 385, pl. 64, figs. 17­ 19. Remarks.-The Texas specimens of D. patulosus are immature forms but they agree with the description given by Elles and Wood of the proximal end and of the character and number of thecae. Horizon.-D. patulosus was collected from one locality within zone 11 ( collec­tion 137) near the middle of the Woods Hollow shale. This species occurs in a single zone in the Glenkiln shales near their upper limit and Ruedemann reports it from the Stringtown shale in Arkansas. DICELLOGRAPTUS PUMILUS Lapworth Dicellograptus pumilus Lapworth, 1876, Cat. West. Scottish Foss., pl. 4, fig. 81. Dicellograptus pumilus Elles and Wood, 1904, Mon. British Grapt., p. 149, texr figs. 92a, b, pl. 21, figs. 3a-£. Remarks.-The Texas specimens agree with the specific description given by Elles and Wood except for a few minor differ­ences. The character and number of thecae are the same as in Elles and Wood's de­scription, and the breadth of the stipes is the same. The stipes of the Texas speci­mens diverge at an angle of 300 to 305 degrees, while in the type forms, the stipes diverge at a 310-degree angle. The stipes are 1 to 2 cm long and are slightly curved. The characteristic wide axil of this species is present in all the Texas specimens. Horizon.-D. pumilus was collected from the middle part of the Maravillas chert, zone 14 (collection 132). Elles and Wood record the species from the lower Hartfell shales of Caradoc age in south­ern Scotland. Thomas and Keble ( 1933) list the species from the lower part of the Bolindian series in the Upper Ordovician of Victoria, Australia. DICELLOGRAPTUS SEXTANS (Hall) Graptolithus sextans Hall, 1847, Paleontology of New York, vol. 1, p. 273, pl. 74, figs. 3a-e. Dicellograptus sextans Elles and Wood, 1904, Mon. British Grapt., pp. 153-155, text figs. 96a-b, pl. 21, figs. la-c. Dicellograptus sextans Ruedemann, 1947, Geo!. Soc. America Mem. 19, pp. 386-387, pl. 64, figs. 28-31. Remarks.-The Texas specimens agree with the specific description by Elles and Wood except that the stipes diverge at an angle of 310 to 315 degrees, while in the typical British material the stipes diverge at an angle of 300 degrees. Horizon.-D. sextans was found in abun­dance in both zones 11 and 12 in the Woods Hollow shale (collections 49, 100, 103, 105, 122, 125, 127, 136, 139, 148, and 150). Graptolite Faunas, Marathon Region Ruedemann records this species from the Normanskill shale of New York, and Elles and Wood report it in the Glenkiln shales in the British Isles. Harris and Thomas ( 1938b) figure it as one of the important forms in the Gisbornian series of the Up­per Ordovician of Victoria, Australia. The species is a common form in the zone of N emagraptus gracilis in the Marathon, Australian, and British successions. DICELLOGRAPTUS SEXTAJ._S var. EXILIS Elles and Wood Pl. 15, fig. 11 Dicellograptus sextans var. exilis Elles and Wood, 1904, Mon. British Grapt., p. 155, text fig. 97, pl. 21, figs. 2a-d. Dicellograptus sextans var. exilis Ruedemann, 1947, Geol. Soc. America Mem. 19, p. 387, pl. 64, figs. 32, 33. Remarks.-The stipes of the Texas speci­mens have, as is true of the English type material. about one.half the width of the true D. sextans but agree with the typical form in all other characters. Horizon.-This variety occurs in the same zones as D. sextans itself-zones 11 and 12 in the Woods Hollow shale (collec­tions 104, 136, and 139). Elles and Wood record the variety from the Glenkiln shale, and Ruedemann has found it in the Nor­manskill shale in New York. DICELLOGRAPTUS SMITHJ Ruedemano Pl. 15, fig. 3b Dicellograptus smithi Ruedemann, 1908, New York State ~Ius. l\'1em. 11, pp. 313-315, text figs. 237, 238, pl, 19, figs.:µ}. Dicellograptus smithi Ruedemann, 1947, Geo!. Soc. America Mem. 19, p. 388, pl. 65, figs. 1-13. Remarks.-The Texas specimens agree well with Ruedemann's specific description. Horizon.-D. smithi was found in zones 11 (collections 122 and 139) and 12 (col­lection 136) in the Woods Hollow shale. Ruedemann's type material came from the "Athens" shale near Pratts Ferry, Ala­bama. He also reports it from the Norman­skill shale near Clinton, New Jersey, and from the Womble shale in Arkansas. Geouo DICRANOGRAPTUS Hall, 1865 DICRANOGRAPTUS BREVICAULIS Elleo aod Wood Pl. 15, fig. 2 Dicranograptus brevicaulis Elles and Wood, 1904, Mon. British Grapt., pp. 168-169, text fig. 105, pl. 24, figs. 3a-d. Remarks.-The Texas specimens are very small but agree well with Elles and Wood's specific description. The biserial portion is 2 to 3 mm in length; in the largest Texas specimens, the uniserial por­tion is 5 mm in length and is nearly straight. In the number of thecae (10 to 11 in 10 mm), the character of the thecae, the width of the stipes, and in the angle between the stipes, the Texas specimens agree with the description of the British material. Horizon.-Specimens of D. brevicaulis were collected from the lower part of the Woods Hollow shale zone 11 (collections 104 and 122) . Elles and Wood report the species to be present in the Glenkiln shales of Shropshire and to be abundant in the same shales in southern Scotland. Harris and Thomas ( l 938b) figure the species as a common form in the Upper Ordovician, Gisbornian series of Victoria, Australia. D. brevicaulis occurs with Nemagraptus gracilis and Dicellograptus sextans in the British, Marathon, and Victorian se­quences. DICRANOGRAPTUS CONTORTUS Ruedemann Dicranograptus contortus Ruedemann, 1908, New York State Mus. Mem. 11, p. 337, text figs. 275-278, pl. 23, fig. 9. Dicranograptus contortus Ruedemann, 1947, Geo!. Soc. America Mem. 19, p. 389, pl. 65, figs. 14­ 36. Remarks.-The Texas specimens agree well with Ruedemann's specific description except that the width of the stipes is slightly less. The stipes of the Texas speci­mens are 0.7 mm wide in the biserial and 0.6 mm wide in the uniserial portion com­pared to 0.8 mm and 0.7 mm width for the same portions of the type specimens. Horizon .-A few specimens of this spe­cies were collected from one locality (col­lection 104) which is in the lower part of the Woods Hollow shale, zone 11. Ruede­ 'i8 Bureau of Economic Geology, The University of Texas mann's types came from the Normanskill shale at Kenwood, New York. He also re· cords the species from the Hailey quad­rangle, Idaho, and from the shale of Three Mile Hill at Bay of Exploits, Newfound­land. DICRANOGRAPTUS NICHOLSONI Hopkinson Pl. 17, fig. 6 Dicranograptus nicholsoni Hopkinson, 1870, Geol. Mag., vol. 7, p. 357, pl. 16, fig. 3. Dicranograptus nicholsoni Elles and Wood, 1904, Mon. British Grapt., pp. 171-173, text figs. 108a·e, 109£, g, pl. 25, fi gs. la-b. Dicranograptus nicholsoni Ruedemann, 1947, Geo!. Soc. America Mem. 19, pp. 391-392, pl. 66, figs. 5-11. Remarks.-The Texas specimens agree well with the description by Ruedemann. The length of the biserial portion is but 4 to 5 mm which is slightly shorter than in the British specimens and the width of the biserial portion is but 2 mm while in the British specimens it is 2.5 mm. Ruedemann notes that in many of the American repre­sentatives of this species, the length and width of the biserial portion are less than in the British specimens. In all other char­acters, however, the American and English specimens are the same. Horizon.-Specimens of D. nicholsoni were collected from the lower part of the Mara villas chert, zone 13 (collections 134 and 134A). Ruedemann states that the typical form of this species is found in the Utica shale in New York and that it is extremely common in the middle horizon of the Utica shale. He also records the species from the Snake Hill shale and Indian Ladder beds in New York and the Fulton shale of the Eden group at Cincin­nati. Elles and Wood report D. nicholsoni to be an abundant fossil in Great Britain near the top of the Glenkiln shales and in the lowest beds of the Hartfell shales and to be especially abundant and well pre­served in the zone of Climacograptus wil­soni. Harris and Thomas ( 1938b) figure D. nicholsoni as a characteristic form of the Upper Ordovician, Eastonian series of Victoria, Australia. DICRANOGRAPTUS NICHOLSONI var. GENICULATUS Ruedemann and Decker Pl. 17, fig. 8 Dicranograptus nicholsoni var. geniculatus Ruede­mann and Decker, 1934, Jour. Paleont., vol. 8, pp. 312-313, pl. 41, figs. 8, Ba. Dicranograptus nicholsoni mut. geniculatus Ruedemann, 1947, Geol. Soc. America Mem. 19, p. 393, pl. 66, figs. 21-24. Remarks.-The Texas specimens agree fully with Ruedemann's specific descrip· ti on. Horizon.-Specimens of this form were collected from the basal beds of the Mara· villas chert, zone 13 (collections 73 and 134A). Ruedemann states that D. nichol­soni mut. geniculatus is especially common in the upper part of the Stringtown shale in the Oklahoma part of the Ouachita Moun­tains and has been found in tht lower part of the Viola limestone at several localities. The writer collected this form from the upper part of the Womble shale in Ar­kansas. Family DIPLOGRAPTIDAE Lapworth, 1873 Subfamily CLIMACOGRAPTINAE Frech, 1897 Genus CLIMACOGRAPTUS Hall, 1865 CLIMACOGRAPTUS ANTIQUUS Lapworth Clz'.macograptus antiquus Lapworth, 1873, Geol. Mag., vol. 10, p. 134 (nom. nud.) . Climacograptus coelatus Lapworth, 1873, Cat. West. Scottish Foss., p. 6, pl. 1, fig. 56. Climacograptus antiquus Elles and Wood, 1906, Mon. British Grapt., pp. 199-200, text figs. 130a-d, pl. 27, figs. 4a-e. Climacograptus antiquus Ruedemann, 1947, Geol. Soc. America Mem. 19, pp. 422-423, pl. 71, figs. 44-48. Remarks.-The Texas specimens agree closely with the specific description by Elles and Wood. Horizon. -Ruedemann (in Sellards, 1933) first reported C. antiquus from the Marathon region. The writer collected it from the basal beds of the Maravillas chert, zone 13 (collections 73, 106, 134, 134A, and 135) . Ruedemann reports the species from the Glenogle shale in British Colum­bia and the Stringtown shale in Oklahoma. The writer has identified it in a collection from the upper part of the Womble shale in Arkansas. Elles and Wood record the Graptolite Faunas, Marathon Region species from the Glenkiln shales and their equivalents in southern Scotland, North Wales, and northern Ireland. Thomas and Keble (1933) list C. antiquus from the Gisbornian series of the Upper Ordovician of Victoria, Australia. CLIMACOCRAPTUS ANTIQUUS var. BURSIFER Elles and Wood Climacograp!us antiquus Lapworth var. bursi/er Elles and Wood, 1906, Mon. British Grapt., p. 201, text figs. 13la, b, pl. 27, figs. 6a-d. Remarks.-A few specimens were col­lected in the Marathon succession which agree well with the description of this va­riety by Elles and Wood except that the Texas specimens have even more closely set thecae (14 to 15 in 10 mm) than the Eng­lish forms ( 12 to 14 in 10 mm) . Horizon.-Specimens of this variety were collected from the upper part of the Woods Hollow shale, zone 12 (collections 94A and 94C). Elles and Wood record it from the Glenkiln shales and their equiv­alents in southern Scotland and Wales. Thomas and Keble (1933) list the variety from the Gisbornian series of the Upper Ordovician of Victoria, Australia. CLIMACOCRAPTUS BICORNIS (Hall) Pl. 16, figs. 10, 11 ; Pl. 19, fig. 4 Graptolithus bicornis Hall, 1847, Paleontology of New York, vol. 1, p. 268, pl. 73, figs. 2a-s. Climacograptlls bicornis Elles and Wood, 1906, Mon. British Grapt., pp. 193-195, text figs. 126a-d, pl. 26, figs. 8a-f. Climacograptus bicornis Ruedemann, 1947, Geo!. Soc. America Mem. 19, p. 425, pl. 72, figs. 44­ 52. Remarks.-The Texas specimens agree closely with the specific description by Elles and Wood and they all have stout spines up to 1 cm long projecting from thP and thl'. Horizon.--C. bicornis is a characteristic species in the upper beds of the Woods Hollow shale, zone 12 (collections 87, 94A, 103, and 136), and it is confined to that zone in the Marathon succession. Rue­demann records it from the Normanskill shale in New York and the writer has seen it at the University of Oklahoma in Decker's collections from the Womble shale of Arkansas and the Stringtown shale of Oklahoma. Elles and Wood state that "C. bicornis is an exceedingly abundant fossil in the Glenkiln and lower Hartfell shales" where it ranges from the zone of Nema­graptus gracilis through the zones of Climacograptus pelt if er and C. wilsoni into the zone of Dicranograptus clingani. Thomas and Keble (1933) record C. bicornis as a common species in the Gis­bornian and Eastonian series of the Upper Ordovician of Victoria, Australia. CLIMACOCRAPTUS CAUDATUS Lapwortb Pl. 18, fig. 7 Climacograptus caudatus Lapworth, 1876, Cat. West. Scottish Foss., p. 6, pl. 2, fig. 48. Climacograptus caudatus Elles and Wood, 1906, Mon. British Grapt., pp. 202-203, text figs. 133 a-d, pl. 27, fi gs. 7a-e. Climacograptus caudatus Ruedemann, 1947, Geo!. Soc. America Mem. 19, p. 424, pl. 71, fi gs. 51­ 52, pl. 72, figs. 57-65. Remarks.-The Texas specimens agree closely with the specific description by Elles and Wood. Horizon. -Specimens of C. caudatus were collected from the lower and middle parts of the Maravillas chert, zones 13 and 14 (collections 128 and 132). Ruedemann reports the species in the Magog shale at Magog, Quebec, in the lower part of the Viola limestone in Oklahoma, and in the upper part of the Womble shale near Crys­tal Springs, Arkansas. Elles and Wood record the species from the zone of Dicranograptus clingani in the Hartfell shales in southern Scotland and Ireland, and Harris and Thomas (1938b) figure it as one of the characteristic forms in the Eastonian series of the Upper Ordovician of Victoria, Australia. CLIMACOGRAPTUS EXIMIUS Ruedemann Climacograptus putillus mut. eximius Ruede­mann, 1908, New York State Mus. Mem. 11, p. 420, figs. 378-384, pl. 28, fig. 16. Climacograptus eximius Ruedemann, 1925, New York State Mus. Bull. 262, p. 62. Climacograptus eximius Ruedemann, 1947, Geo!. Soc. America Mem. 19, p. 435, pl. 72, figs. 1-15. Remarks.-The Texas specimens agree fully with Ruedemann's specific descrip­tion. Bureau of EconomU: Geology, The University of Texas Horizon.-Specimens of C. eximius are common in the Woods Hollow shale, zones 11 and 12 (collections 94A, 103, 137, and 139). Ruedemann states that the species is common in the Normanskill shale in New York, and the writer has seen it in Decker's collections from the Stringtown shale of Oklahoma and the Womble shale of Arkansas. CLIMACOGRAPTUS HASTATUS T. S. Hall PL 20, fig. 11 Climacograptus hastata T. S. Hall, 1902, Geol. Survey, New South Wales, p. 5, pl. 14, figs. 1-3. Climacograptus hastatus T. S. Hall var. ameri­canus Ruedemann, 1947 (pars), Geol. Soc. America Mem. 19, p. 427, pl. 73, figs. 8, 9, 13, 17, 19, not figs. 1-7, 10--12, 14-16, 18, 20. Climacograptus tridentatus Sherrard, 1949, Lin· nean Soc. New South Wales, Proc., vol. 74, p. 69, text fig. 12A. Climacograptus hastatus Harris and Thomas, 1955, Min. and Geol. Journ., vol. 5, no. 6, p. 39, figs. 8, 9. Remarks.-The Texas specimens agree closely with the specific description by T. S. Hall. The Texas specimens have two, three, and even four basal spines ( exclud· ing the virgella projection). Sherrard (1949), on Dr. G. L. Elles' identifications, regards Hall's species as a synonym of C. bicornis var. tridentatus. However, none of the published figures nor descriptions of C. bicornis var. tridentatus record a virgellar projection which subordinates the two lat­eral spines. In all of Elles and Wood's (1906, pl. 26, figs. 9a-c) figures of C. bicornis var. tridentatus, the spines are thickened by membrane and are wider than the virgellar projection. In C. hastatus the virgellar projection is the prominent fea­ture and the spines are subordinate. Ruede­mann (1947) includes in his figures of C. hastatus var. americanus forms which may be related to C. bicornis (pl. 73, figs. 14, 15, 16, 18, 20) and some which show no development of spines (pl. 73, figs. 1--4) . Even immature forms of the Texas specimens have spines. The writer considers that Ruedemann's figures 13, 17, and 19 (pl. 73) of C. hastatus var. americanus agree with the specific descrip­tion of C. hastatus by Harris and Thomas, and thus the varietal name may not he needed. Horizon. -Specimens of C. hastatus were collected from the highest beds of the Mara villas chert, zone 15 (collection 60) . Ruedemann recorded his variety from the highest Ordovician horizon near Trail Creek, Blaine County, Idaho. Harris and Thomas record the species from the Eastonian series of the Upper Ordovician in Victoria, Australia. The species appears earlier in the Victorian sequence than it does in the Marathon. CLIMACOGRAPTUS MINIMUS (Carruthero) Pl. 19, fig. 2 Diplograptus minimus Carruthers, 1868, Geol. Mag., vol. 5, p. 125, pl. 5, figs. 12a, b. Climacograptus minimus Elles and Wood, 1906, Mon. British Grap!., pp. 191-192, text figs. 124a-d, pl. 27, figs. la-g. Remarks. -The rhabdosomes of the Texas specimens are small, the largest measuring 1.5 cm in length and 1.8 mm in breadth. Elles and Wood give a range in length of 1 to 3 cm and a maximum breadth of 2 cm for the English speci­mens. The thecae of the Texas specimens number 12 to 14 in 10 mm and their apertural margins are horizontal. Their excavations are not so deep as in the English specimens. The thecal excavations in the English forms occupy fully one­third of the width of the rhabdosome, whereas in the Texas specimens they oc· cupy only about one-fourth the width of the rhahdosome. Elles and Wood give a thecal range of 11 to 14 in 10 mm for the English material. In the character of the proximal end and of the thecae, the Texas specimens agree with the description by Elles and Wood. In the writer's opinion, the Texas specimens, although small, ap­pear to fall within the range in variation of C. minimus. Horizon.-C. minimus is a common form in the middle part of the Maravillas chert, zone 14 (collections 54, 55, 83A, 83B, and 86A). Elles and Wood record the species from the zones of Dicranograptus clingani and Pleurograptus linearis of the Hartfell shales in southern Scotland and Grapwlite Faunas, Marathon Region Wales, and Thomas and Keble (1933) list it from the Eastonian series of the Upper Ordovician of Victoria, Australia. CLIMACOGRAPTUS MISSISSIPPIENSIS Ruedemann PI. 20, fig. 9 C!imacograptus mzsszsszppiensis Ruedemann, 1908, New York State Mus. Mem. 11, pp. 413­ 414, text figs. 366, 367, pl. 28, figs. 12, 13. Climacograptus mississippiensis Ruedemann, 194i, Geo!. Soc. America Mem. 19, pp. 431­ 432, pl. 74, figs. 3-9. Remarks.-The Texas specimens agree closely with Ruedemann's specific descrip­tion. Hori::on.-Specimens of C. mi.ssissip­pien.sis were collected from the highest beds of the Maravillas chert, zone 15 (col­lections 60 and 138). Ruedemann's types came from the Sylvan shale of the Ar­buckle Mountains in Oklahoma, and Rue­demann also records it from the Polk Creek shale and the Bigfork chert in Arkansas. CLIMACOGRAPTCS MODESTUS Ruedemann Climacograptus modestus Ruedemann, 1908, New York State .'.\ius. :\lem. 11, pp. 432--433, text fig5, 400-4D3, pl. 28, fig. 30. Climacograptus modes/us Ruedemann, 1947, Geo!. Soc. America .'.\lem. 19, p 432, pl. 73, figs. 32­ 46. Climacograptus modestus Bulman, 1948, Geo!. Mag., \'Ol. 85, pp. 222-223, text figs. la, b. Remarks.-The Texas specimens agree fully with Ruedemann's specific descrip­tion. The more closely set thecae ( 16 in 10 mm in the Texas specimens) and the blunt squarish appearance of the proximal end distinguish this species from C. scharen­bergi. Hori::on.-Specimens of C. modestus were collected from the upper part of the Woods Hollow shale, zone 12 (collections 94A, 94B, and 94C). Ruedemann records the species from the l\ormanskill shale in 1'\ew York, the upper part of the Wamble shale in Arkansas, and from the "Athens shale" in Virginia and Tennessee. Bulman reports it with Nemagraptus gracili.s from the Rorrington flags on Sky Brook, Shropshire. CLIMACOGRAPTUS MODESTUS nr. MERIDIONALIS Ruedemann Climacograptus modestus var. meridionalis Ruedemann, 1947, Geo!. Soc. America Mem. 19, p. 433, pl. 73, figs. 47, 48. Remarks.-The Texas specimens agree closely with Ruedemann's description ex­cept that the thecae number 14 in 10 mm, while in the type material the thecae num­ber 10 to 13 in 10 mm. Horizon.-Specimens of this variety were collected from the lower part of the Woods Hollow shale, zone 11 (collection 137). Ruedemann's types came from the "Athens shale" near Bristol, Tennessee, and he also reports it from the "Athens shale" near Calera, Alabama. The form occurs with Nemagraptus gracil£s and its associates in Texas, Tennessee, and Ala­bama. CLIMACOGRAPTUS PARVUS Hall Pl. 16, fig. 12 Climacograptus parvus Hall, 1865, Canadian Organic Remains, p. 57 ( nom. nud.). Climacograptus parvus Hall, 1868, New York State Cab. Nat. Hist., 20th Ann. Rept., p. 224. Climacograptus parvus Ruedemann, 1947, Geo!. Soc. America Mem. 19. pp. 433-434, pl. 74, figs. 10--26. Remarks.-The rhabdosomes of the Texas specimens are small, up to 20 mm long and 1.7 mm wide, but these measure­ments fall within the range in variation given by Hall in his specific description. The Texas specimens agree well with Hall's specific description in all other characters. Horizon.-C. parvus was collected from zones 11 (collection 137) and 12 ( collec­tions 94-A, 94B, and 136) in the Woods Hollow shale. The species is one of the most common and widespread graptolites in the upper part of the Middle Ordovician in North America. Ruedemann records it from the Normanskill shale in New York, the Stringtown shale of Oklahoma, the Womble shale of Arkansas, and from locali­ties in Newfoundland, Maine, Virginia, Nevada, and Washington. CLIMACOGRAPTUS PUTILLUS (Hall) Graptolithus putillus Hall, 1865, Canadian Or­ganic Remains, pp. 27, 44, pl. A, figs. 10--12a. Bureau of Ecorwmic Geology, The University of Texas Climacograptus putillus Ruedemann, 1925, New York State Mus. Bull. 262, p. 60. Climacograptus putillus Ruedemann, 1947, Geo!. Soc. America Mem. 19, pp. 434--435, pl. 72, figs. 29-42. Remarks.-The Texas specimens are small, 5 to 7 mm in length and 1 mm wide, but still fall within the range of the meas­urements given by Ruedemann (1947) for C. putillus. In number of thecae ( 12 to 14 in 10 mm) and in character of the thecae, the Texas specimens agree with the description by Ruedemann. Horizon.-Specimens of C. putillus were collected from the uppermost beds in the Maravillas chert, zone 15 (in collections 60 and 147). Ruedemann records it from the Maquoketa shale near Maquoketa, Iowa, and from the Sylvan shale of Oklahoma. CLIMACOGRAPTUS RIDDELLENSIS Harris Pl. 14, figs. 9, 10 Climacograptus riddellensis Harris, 1924, Royal Soc. Victoria, Proc. (n.s.), vol. 36, pp. 100­101, pl. 8, figs. 11, 12. Remarks.-The Texas specimens agree well with the specific description by Harris except that the thecae number 11 to 12 in 10 mm while in the Australian specimens they number 10 to 11in10 mm and, rarely, as many as 13 in 10 mm. The characteristic wide, semicircular thecal excavations can easily be seen in the specimens preserved in low relief in limestone. Horizon.-Specimens of C. riddellensis were collected from the basal beds of the Woods Hollow shale, zone 10 (collections 46 and 46A), and from higher in the same formation in zone 11 (collection 137). Harris ( 1935) lists the species as a com­mon form in the zone of Glyptograptus teretiusculus, the highest zone in the Mid· dle Ordovician of the Victoria, Australia, sequence. Thomas and Keble ( 1933) list it as present in collections from the Gisbor­nian series of the Victorian Upper Ordo­vician as well. The species has a similar range (zones of G. teretiusculus and Nema­graptus gracilis) in both the Marathon and Victorian successions. CLIMACOGRAPTUS SCALARIS var. MISERABILIS Elles and Wood? Remarks.-The Texas specimens are poorly preserved and some details can not be seen. The rhabdosomes agree with Elles and Wood's (1906, Mon. British Grapt., pp. 186-187, text figs. 120a-c, pl. 26, figs. 3a-h) description in size (1 to 1.5 cm in length and no more than 1 mm in breadth), in number of thecae (10 to 11 in IO mm), and in possessing a complete septum. The thecae have vertical outer edges and hori· zontal apertural margins, which agree with Elles and Wood's description, but the size and shape of the excavations are obscure. Also, the nature of the proximal end is obscure. The Texas specimens agree with the description of C. scalaris var. miser­abilis in general aspect, but the preserva­tion is so poor that they are only tentatively referred to this variety. Horizon.-Specimens provisionally re­ferred to C. scalaris var. miserabilis were collected from one locality (collection 147) which is in the highest beds of the Mara· villas chert, zone 15. They are associated with Dicellograptus complanatus and D. complanatus var. ornatus. Elles and Wood state that the variety miserabilis is most abundant in the zone of Dicellograptus complanatus and that it is also found in the zone of Dicellograptus anceps and a few individuals survive into the lowest beds of the Silurian. Thomas and Keble ( 1933) list the variety miserabilis from the highest beds of the Bolindian series of the Upper Ordovician of Victoria, Australia. CLIMACOGRAPTUS SCHARENBERGI Lapworth Climacograptus scharenbergi Lapworth, 1876, Cat. West. Scottish Foss., p. 6, pl. 5, fig. 35. Climacograptus scharenbergi Elles and Wood, 1906, Mon. British Grapt., pp. 206-208, text figs. 139a-c, pl. 27, fig. 14a-e. Climacograptus scharenbergi Ruedemann, 1947, Geo!. Soc. America Mem. 19, pp. 438-439, pl. 74, figs. 41-54. Climacograptus scharenbergi Bulman, 1947, Cara. doc (Balclatchie) Grapt., pp. 65-70, text figs. 34-38, pl. 7, figs. 1-10, pl. 8, figs. 1, 5-7. Remarks.-The Texas specimens agree closely with the specific description by Elles and Wood. Graptolite Faunas, Marathon Regi-On Horizon.-Specimens of C. scharenbergi were collected from the lower part of the Maravill!ls chert, zone 13 (collections 73, 134, and 134A). Ruedemann records the species from the Normanskill shale in New York and the Magog shale in Quebec. Elles and Wood state that it is a long· ranging species in the British Isles, rang· ing from the zone of Didymograptus bifi­dus in the upper part of the Arenig series through the zone of Climacograptus wilsoni in the lower part of the Hartfell shales. The maximum number of individuals was col­lected from the younger horizons. CLIMACOGRAPTUS SCHARENDERGI cf. var. STENOSTOMA Bulman Pl. 15, fig. 6 Climacograptus scharenbergi var. stenostoma Bulman, 1947, Caradoc (Balclatchie) Grapt., p. 70, pl. 7, figs. 11, 12, pl. 8, figs. 2-4, 8. Remarks.-The Texas specimens have smaller dimensions than the types. The largest of the Texas forms is 7 mm in length and has a maximum width of 0.9 mm compared to a length of 7 mm and a maximum width of 1.1 mm for the largest of the English specimens. The free ventral edges of the thecae show the same amount of curvature as do the English specimens, but the detail of the apertural excavations is obscure because of the poor preserva­tion. The thecae number 14 to 15 in 10 mm in the Texas specimens, while they are somewhat less closely set in the English material. The Texas specimens are defi­nitely of the C. scharenbergi type and agree in general aspect with Bulman's variety stenostoma but are slightly smaller and are not well enough preserved to reveal all the detail of the thecae. Horizon.-Specimens of this form were collected from the Woods Hollow shale, zones 11 and 12 (collections 122, 127, and 150). Bulman's types of C. scharenbergi var. stenostoma came from the Balclatchie beds of Caradoc age exposed in Laggan Burn, Ayrshire, Scotland. CLIMACOGRAPTUS SPINIFERUS Ruedemann Climacograptus typicalis mut. spini/er Ruede­ rnann, 1908, New York State Mus. Mem. 11, pp. 411-412, text fig. 236, pl. 28, figs. 8, 9. Climacograptus spini/erus Ruedemann, 1912, New York State Mus. Bull. 162, p. 84. Climacograptus spini/erus Ruedernann, 1947, Geol. Soc. America Mern. 19, p. 439, pl. 75, figs. 1-7. Remarks.-The Texas specimens agree fully with Ruedemann's specific descrip­tion. Horizon.-Specimens of C. spiniferus were collected from the lower part of the Maravillas chert, zone 13 (collections 86B and 134) . Ruedemann states that this spe­cies is a common and characteristic form in the Canajoharie shale in New York, and that it also occurs in the Snake Hill shale and Schenectady beds in the same State and in the lower part of the Viola limestone in the Arbuckle Mountains of Oklahoma. CLIMACOGRAPTUS TUBULIFERUS Lapworth Pl. 19, fig. 5 Climacograptus tubuliferus Lapworth, 1876, Cat. West. Scottish Foss.. pl. 2, fig. 49. Climacograptus tubuliferus Elles and Wood, 1906, Mon. British .Grapt., pp. 203-204, text figs. 134a-c, pl. 27, figs. 8a-d. Climacograptus tubuliferus Ruedemann, 1947, Geol. Soc. America Mem. 19, p. 440, pl. 75, figs. 54-56. Remarks.-The Texas specimens agree well with the specific description by Elles and Wood. Horizon.-Specimens of C. tubuliferus were collected from the middle part of the Maravillas chert, zone 14 (collections 45, 55, 83B, 86A, and 93). Ruedemann re­cords the species from the Polk Creek shale and the Talihina chert in Oklahoma. Elles and Wood report the species to be fairly common in the zone of Pleurograptus line­aris and to be rare in the zone of Dicrano­graptus clin{rnni in the British Isles. Thomas and Keble (1933) list C. tubuli­ferus from the Eastonian series of the Upper Ordovician in Victoria, Australia. The same species occurs with the same as­sociates ( Orthograptus quadrimucronatus, Dicellograptus forchammeri, and Ortho­graptus truncatus) in the Marathon, Vic­torian, and British sequences. CLIMACOGRAPTUS TYPICALIS Hall Climacograptus typicalis Hall, 1865, Canadian Organic Remains, pp. 27, 28, 57, pl. A, figs. 1-9. Bureau of Economic Geology, The University of Texas Climacograptus typicalis Ruedemann, 1947, Geo!. Soc. America Mem. 19, pp. 44-0-441, pl. 75, figs. 27-38, not pl. 91, fig. 8. Remarks.-The Texas specimens are all small yet still fall within the measurements given in the description by Ruedemann. The largest specimens measure 3.0 cm in length and 2.2 mm in width. The thecae in all of the Texas specimens number 11 to 13 in 10 mm and agree with the descrip· tion of the type material. Horizon.-C. typicalis was collected from the lower and middle parts of the Mara villas chert, zones 13 and 14 ( collec· tions 73, 13lA, and 133) . Ruedemann re· cords the species from the Utica and Frank· fort shales in New York, the Eden shale at Covington, Kentucky, the Platteville and Galena limestones of Minnesota, the lower part of the Viola limestone of Oklahoma, and the Womble shale of Arkansas. CLIMACOGRAPTUS TYPICALIS var. CRASSIMARGINALIS Ruedemann and Decker Pl. 17, figs. l, 2 Climacograptus typicalis var. crassimarginalis Ruedemann and Decker, 1934, Jour. Paleont., vol. 8, pp. 322-323, 325, pl. 43, figs. 8, 9, 12, 12a. Climacograptus typicalis var. crassimarginalis Ruedemann, 1947, Geo!. Soc. America Mem. 19, pp. 441-442, pl. 73, figs. 23-26, pl. 75, fig. 46, pl. 91, fig. 8. Remarks.-The Texas specimens of this spined variety of C. typicalis are all small and no complete rhabdosomes were found. However, the measurements of them do fall within the range of variation of C. typicalis, and the diagnostic character of this va· riety, the sharp flange that projects out from each thecae, is well developed. One of the forms figured by Ruedemann and Decker as Amplexograptus amplexicaulis from the Viola limestone (Ruedemann and Decker, 1934, pl. 42, figs. 1, la) should be referred to this variety of C. typicalis. Horizon.-This form is a characteristic element of zone 13, the lower part of the Maravillas chert (collections 106, 128, 133, and 135) . It is common in the lower part of the Viola limestone in the Arbuckle Mountains in Oklahoma, and it has been recorded from the Platteville limestone near Dixon, Illinois (Ruedemann, 1947). CLIMACOGRAPTUS eC. C. ULRICHI Ruedemana Remarks.-The Texas specimens tenta· tively referred to the species C. ulrichi are poorly preserved so that details of the the· cae cannot be seen. The rhabdosomes are small, 10 to 12 mm in length, and 1.5 to 1.8 mm in width. The sicula end is narrow and pointed, and a free prolongation of the nemacaulis is present. The thecae number 10 to 12 in 10 mm. In all of these measure· ments, the Texas specimens agree with Ruedemann's description ( 1947, Geol. Soc. America Mem. 19, p. 443, pl. 91, figs. 9-12). However, the details of the thecae must be seen to identify the species defi· nitely, and they cannot be seen in these specimens. Therefore, the Texas specimens can only be compared to C. ulrichi. Horizon.-The specimens tentatively re· £erred to C. ulrichi were collected from the uppermost beds of the Maravillas chert, zone 15 (collections 138 and 147). Ruede­mann states that the species C. ulrichi is widely distributed throughout the South­west. The type specimens were obtained by Ulrich from the Maquoketa shale at Spencer, Missouri, and Decker (1935, p. 708) has cited the species from the Sylvan shale of Oklahoma and the Polk Creek shale of Arkansas. Subfamily DIPLOGRAPTINAE Lapworth, 1873 Genus DIPLOGRAPTUS McCoy, 1850 DIPLOGRAPTUS CRASSITESTUS Ruedemann PI. 20, figs. 7, 8 Diplograptus crassitestus Ruedemann. 1908, New York State Mus. Mem. 11, pp. 334-335, text figs. 299-300, pl. 25, fig. 6. Diplograptus (Mesograptus) crassitestus Ruede­mann, 1947, Geo!. Soc. America Mem. 19, pp. 415-416, pl. 71, figs. 3-9. Remarks.-The Texas specimens are nearly identical to the type specimens from Oklahoma except that the length and width are slightly less. The rhabdosomes have a length of 32 to 38 mm with a width at the distal end of 1.3 to 1.8 mm. The thecae of Graptolite Faunas, Marathon Region the Texas specimens number 9 to 10 in 10 mm, whereas the thecae number 7 to 10 in 10 mm in the type material. Horizon.-This species is common in zone 15 (collections 60, 138, and 147), the highest beds of the Maravillas chert. The species is also common in the Sylvan shale in the Arbuckle Mountains in Oklahoma and in the Polk Creek shale in the Ouachita Mountains in Arkansas. DIPLOGRAPTUS MULTIDE.1\'S Elles and Wood Pl. 16, fig. 2; Pl. 19, fig. 6 Dipl.ograptus (Mesograptus) rnultidens Elles and Wood, 1907, Mon. British Grapt., pp. 261-262, text fig. 178, pl. 31, figs. 9a-d. Dipl.ograptus (Mesograptus) multidens Ruede­mann, 1947, Geo!. Soc. America l\iem. 19, p. 420, pl. 71, figs. 15, 16. Remarks.-The Texas specimens agree well with the specific description by Elles and Wood. Horizon.-Specimens of D. multidens were collected from one locality ( collec­tion 87) which is in the upper part of the Woods Hollow shale, zone 12. It is associ­ated with Climacograptus bicornis, Ortho­graptus calcaratus var. acutus, and Am­plexograptus cf. A. perexcavatus. Elles and Wood record D. multidens from the high­est beds of the Glenkiln shale and the lowest of the Hartfell shale, where it occurs with the same associates as in the Marathon re­gion. Harris and Thomas (1938b) figure the species as one of the common forms in the Gisbornian series and state that it is one of the characteristic species of the upper part of that series in Victoria, Australia. DIPLOGRAPTUS MULTIDESS var. DIMl1'"UTUS Ruedemann Dipl.ograptus (Mesograptus) multidens var. di­ m.inutus Ruedemann, 1947, Geo!. Soc. America l\lem. 19, p. 420, pl. 71, figs. 20-23. Remarks.-The Texas specimens agree well with Ruedemann's description of this small variety. None of the rhabdosomes measure more than 15 mm in length and 1.8 mm in width. Except for the size dimen­sions, all characters of the variety are the same as those of the typical form. Horizon.-Specimens of this variety were collected from the upper part of the Woods Hollow shale, zone 12 (collections 87, 94A, and 94C), where it is associated with the typical form of the species and with Amplexograptus cf. A.. perexcavatus and Orthograptus calcaratus var. acutus. Ruedemann described the variety from "Ordovician shale of Normanskill age" at the southwest feeder of Portland Creek Pond, Newfoundland. DIPLOGRAPTUS MINUTUS Berry, n. sp. Pl. 18, figs. 2, 3 Description.-The rhabdosomes are small, measuring 10 to 14 mm in length and 1.1 mm in width at the proximal end but widening to 2.0 mm distally. The sicula was not observed. The proximal end is rounded and possesses a short virgella. A septum begins between the fifth and sixth thecal pair. The thecae number 11 to 12 in 10 mm, have a Climacograptus aspect in the proximal region of the rhabdosome and a gentle sigmoid curvature in the distal part. They overlap one-third to one-half their length and have wide apertural mar­gins. Horizon.-Specimens of this species were obtained from the upper part of the Maravillas chert, zone 14 (collection 45). Holotype.-Yale Peabody Museum No. 20256. Genus AMPLEXOGRAPTUS Elles and Wood, 1907 AMPLEXOGRAPTUS CONFERTUS (Lapworth) Pl. 14, figs. 1, 2 Clim.acograptus confertus Lapworth, 1875, Quart. Jour. Geol. Soc., vol. 31, p. 655, pl. 34, figs. 4a-f. Diplograptus ( Amplexograptus) con/ertus Elles and Wood, 1907, Mon. British Grapt., pp. 269­ 270, text figs. 185a-c, pl. 31, fi gs. 18a-e. Amplexograptus confertus Harris and Thomas, 1935, Royal Soc. Victoria, Proc. (n.s.), vol. 47, pp. 300-301, fig. 1, nos. 14a, b, fig. 3, nos. 21-26. Remarks.-The Texas specimens agree with the description of the Australian forms by Harris and Thomas. However, the thecae are fewer (14 to 10 in 10 mm) than in the English types (16 to 12 in 10 mm). Some of the Texas specimens are Bureau of EcorwmU: Geology, The University of Texas preserved in low relief in limestones, and in these, the apertural excavations are slightly wider and not quite so deep as in the British types which are preserved flat­tened in shale. These slight variations may be due to the differences in preservation. The details of the thecae of the Texas speci­mens which are preserved flattened agree with the figures of the thecae of the British material. The thecae of the Texas speci­mens are fewer than the British types, but in most of the specimens the number of thecae fall within the range of variation of the number of thecae per 10 mm given by Elles and Wood. Therefore, the writer in­cludes his forms under the species A. con­f ertus. Horizon.-Specimens of A. confertus were collected from zone 10, the highest beds of the Fort Pena formation and the lowest beds of the Woods Hollow shale (collections 38, 46, 46A, 81, 85, and 92). A. confertus is a diagnostic element of zone 10. Harris ( 1935) lists the species as com­mon in the zone of Diplograptus decoratus of the Middle Ordovician of Victoria, Aus­tralia. Elles and Wood record it from the zone of Didymograptus bifidus (Lower Llanvirn) in Great Britain. The species occurs much earlier in the British sequence than it does in the Marathon and Aus­tralian sequences. AMPLEXOGRAPTUS cf. A. DIFFERTUS Harris and Thomas Remarks.-None of the rhabdosomes of the Texas specimens is longer than 1.5 cm. and they attain a width of 2.0 mm at a distance of 7.0 mm from the proximal end and widen to 2.5 mm at a distance of 10 mm from the proximal end. The thecae number 12 to 14 in 10 mm. The Texas specimens are not so long as the maximum length of the forms described by Harris and Thomas (1935, Royal Soc. Victoria, Proc. (n. s.), vol. 47, p. 301, fig. 1, no. 15, fig. 3, nos. 27-31), and the thecae are slightly closer packed (12 to 14 in 10 mm, whereas they number 10 to 13 in 10 mm in the Australian material). The Texas specimens agree in the character of the thecae with the description of those of A. difjertus (the apertures are inclined with notably thickened margins and they oc­cupy one-third the width of the rhabdo­some and one-fourth of the free edge). Although the Texas specimens are slightly smaller and have slightly closer packed thecae, they agree in all other respects with A . di/Jertus and should be compared to it. Horizon.-A few specimens of this form were collected from zone 10. It was identi­fied in collection 46 from the basal beds of the Woods Hollow shale and in collection 85 from the highest beds of the Fort Pena formation. Harris and Thomas report the species to be common in the zone of Diplo­graptus decoratus in the Middle Ordo­vician in Victoria, Australia. AMPLEXOGRAPTUScf. A. PEREXCAVATUS (Lapworth) PI. 16, figs. 8, 13 R emarks.-The Texas specimens are poorly preserved and the proximal ends cannot be seen. The fragments of the rhab­dosomes seen are short and broad, 1 to 2 cm in length and 2.2 to 2.7 mm in breadth. The thecae number 12 to 14 in 10 mm, whereas Elles and Wood (1907, p. 267) give a range of 12 to 16 in 10 mm for the British specimens. In the reverse aspect the thecae appear similar to those of Orth-0­graptus. In this view, the thecal overlap is conspicuous. The ventral wall extends al­most to the center of the rhabdosome and the thecae may be seen to overlap for one­half their length. Also, the alternating ar­rangement of the thecae is clear. In size and shape of the rhabdosome and in num­ber and character of the thecae, the Texas specimens agree with the specific descrip­tion of A. perexcavatus by Elles and Wood ( 1907, Mon. British Grapt., pp. 267-269, text figs. 184a-d, pl. 31, figs. 15a-d), but since the proximal ends cannot be seen, definite specific identification is not war­ranted. Horizon.-The specimens tentatively re­ferred to A. perexcavatus were collected from the highest beds in the Woods Hollow shale, zone 12 (collection 87). Elles and Graptolite Faun.as, Marathon Region Wood report that A. perexcavatus is a very abundant fossil in the Glenkiln shales of Scotland and Wales, where it ranges from the zone of N emagraptus gracilis to the zone of Climacograptus wilsoni. Elles (1925) lists it as a common fossil in the zone of Climacograptus bicomis var. pelti­Jer where it is associated with C. scharen­bergi, Dicellograptus sextans, and Ortho­graptus calcaratus var. acutus. The Texas specimens tentatively referred to A. per­excavatus were found in a similar as­semblage. Harris and Thomas (1938b) figure A. perexcavatus as a common form in the Gisbornian series of the Upper Ordo­ vician of Victoria, Australia. Genus GLYPTOGRAPTUS Lapworth, 1873 GLYPTOGRAPTUScf.G.AUSTRODE:,"TATUS (Harris and Keble) Pl. 13, figs. 2, 3 Remarks.-The rhabdosomes of the Texas specimens are longer and thinner than the Australian form described by Harris and Keble (1932, text figs. 1-4, pl. 5, figs. 4-5) , since they average about 1.5 cm in length and widen from 1.5 mm at the base to 1.8 mm distally, whereas in the Australian material the rhabdo­somes average about 1.0 cm in length and widen to 2 mm distally. The thecae in the Texas specimens number 14 in 10 mm, are 1.5 mm long and 0.3 mm wide, and overlap one-half their length. In the Australian forms, the thecae number 12 to 14 in 10 mm, are 1.5 mm long and 0.5 mm wide, and overlap one-half to two­thirds of their length. In all other respects the Texas specimens agree closely with the specific description of G. austrodentatus by Harris and Keble. Horizon. -The forms tentatively re­red to G. austrodentatus are rare in the lower part of the Fort Pena formation, zone 8 (collections 10, 95, 98A, and 112), and are common in the upper part of that for­mation, zone 9 (collections 15, 28, 117, 117A, and 152). In Australia G. austro­dentatus is a common species in the lowest zone of the Middle Ordovician, and it is the name-giving species to that zone. It is associated with H allograptus etheridgei, Cryptograptus schajeri, and Trigonograp­tus ensiformis in Australia, and the form herein tentatively referred to G. austroden· tatus occurs with the same associates. A closely similar species, G. dentatus, is the characteristic form of graptolite bed 7 of the Deepkill shale in New York, and Ray· mond's (1914) zone D of the Levis shale in Quebec. GLYPTOGRAPTUS INTERSITUS Harr;s and Thomas Glyptograptus intersitus Harris and Thomas, 1935, Royal Soc. Victoria, Proc. (n.s.), vol. 47, pp. 296-297, fig. 1, nos. lla-e, fig. 3, nos. 7-10. Remarks.-The Texas specimens agree fully with the specific description by Har­ris and Thomas. Horizon.-Specimens of G. intersitus were collected from the upper part of the Fort Peiia formation, zone 9 (collections 13, 15, 16, and 28). In Victoria, Australia, the species is abundant in, and typical of, the second zone (to which it is the name­giving species) of the Middle Ordovician. It also occurs in the highest beds of the zone below (zone of Glyptograptus austro­dentatus) and the lowest beds of the zone above (zone of Diplograptus decoratus) . GLYPTOGRAPTUS TERETIUSCULUS (Hisinger) Pl. 14, figs. 3-5, 8; PI. 16, fig. 5 Prionotus teretiusculus Risinger, 1840, Lethaea Suecica, Suppl. II, p. 5, pl. 38, fig. 4. Diplograptus ( Glyptograptus) teretiusculus Elles and Wood, 1907, Mon. British Grapt., pp. 250­252, text figs. l 7la-d, pl. 31, figs. la-e. Diplograptus ( Glyptograptus) teretiusculus Ruedemann, 1947, Geol. Soc. America Mem. 19, pp. 408-409, pl. 69, figs. 35-45. Remarks.-As Elles and Wood indicate, the rhabdosomes of G. teretiusculus display a considerable variation in shape. Many of the Texas specimens are thinner than the British types but agree in all other char· acters with the specific description by Elles and Wood. Some of the Texas specimens agree closely in all dimensions with Elles and Wood's specific description. Still others of the Texas specimens are wider than the British material but compare favorably in size with Swedish material. However, the Bureau of Ecorwmic Geology, The University of Texas thecae of these latter Texas forms number but 9 in 10 mm while the thecae of the Swedish and English forms number 10 to 14 in 10 mm. The Texas specimens with wide rhabdosomes and fewer thecae have been identified as G. cf. G. teretiusculus. Horizon.-G. teretiusculus is a common form in the Woods Hollow shale. It occurs in both zones 11 (collections 104, 137, and 150) and 12 (collections 87, 94C, 105, 127, and 136). The specimens referred to G. teretiusculus are the characteristic forms of zone 10 and give their name to that zone. They were collected from the uppermost beds of the Fort Pena formation ( collec­tions 81, 85, 92, and 126). G. teretiusculus is common in the Normanskill shale in New York according to Ruedemann, and he further states that it is known from the Womble shale in Arkansas, the Stringtown shale in Oklahoma, and localities in British Columbia, Nevada, New Jersey, Quebec, and Newfoundland. In Great Britain, the species is characteristic of horizon 8 (the zone of G. teretiusculus), but it ranges through zones 9 (zone of Nemagraptus gracilis) and 10 (zone of Mesograptus multidens) to zone 11 (zone of Climaco­graptus wilsoni). Harris (1935) lists G. teretiusculus as a very common species in the highest beds of the Middle Ordovician in Victoria, Australia, and it gives its name to a zone which comprises the youngest beds of the Victorian Middle Ordovician. Thomas and Keble (1933) record the spe­cies from the Gisbornian series of the Vic­torian Upper Ordovician. G. teretiusculus is a common and long-ranging species in the Marathon, Victorian and British grap­tolite sequences, and it is the characteristic form of the zone below that of Nema­graptus gracilis in all three areas. GLYPTOGRAPTUS TERETIUSCULUS var. EUGLYPHUS (Lapworth) PL 15, fig. 8 Diplograptus (Glyptograptus) euglyphus Lap­worth, 1880, Ann. Mag. Nat. Hist., vol. 5, p. 166, pl. 4, figs. 14a-e. Diplograptus (Glyptograptus) teretiusculus var. euglyphus Elles and Wood, 1907, Mon. British Grapt., p. 252, text fig. 172, pl. 31, figs. 2a-d. Diplograptus (Glyptograptus) euglyphus Ruede­mann, 1947, Geol. Soc. America Mem. 19, pp. 405-406, pl. 69, figs. 46-50, 55-59. Remarks.-The Texas specimens agree closely with the varietal description by Elles and Wood. Horizon.-This variety is a fairly com­mon fossil in the Woods Hollow shale. It is found in both zones 11 (collections 104, 148, and 150) and 12 (collections 87, 94A, 94B, 94C, 100, and 127). Elles and Wood state that the variety is fairly com­mon in the zone of N emagraptus gracilis in the Glenkiln shales of southern Scotland. Harris and Thomas (1935) refer a form to this variety which is common in the upper­most zone (zone of G. teretiusculus) of the Middle Ordovician of Victoria, Australia. GLYPTOGRAPTUS TERETIUSCULUS var. PYGMAEUS (Ruedemann) Diplograptus euglyphus var. pygmaeus Ruede­ mann, 1908, New York State Mus. Mem. 11, p. 371, text figs. 317, 318, pl. 25, fig. 24. Diplograptus (Glyptograptus) euglyphus var. pygmaeus Ruedemann, 1947, Geol. Soc. Amer­ ica Mem. 19, p. 406, pl. 69, figs. 51-53. Remarks.-The Texas specimens agree closely with Ruedemann's figures of Diplo­graptus (Glyptograptus) euglyphus var. pygmaeus. The writer considers the form G. euglyphus to be a variant of G. teretius­culus and not a distinct species, and the forms Ruedemann considered to be varie­ties of G. euglyphus belong to the complex of forms related to G. teretiusculus. The variety pygmaeus is similar to the variety euglyphus except that the thecae number 14 to 15 in 10 mm (in var. euglyphus they measure 9 to 11 in 10 mm) and the rhab­dosome is much thinner (0.9 to 1.4 mm wide whereas var. euglyphus is 1.4 to 2.2 mm in width). Horizon.-Specimens of this variety were collected from the upper part of the Woods Hollow shale, zone 12 (collections 94A, 105, and 127). Ruedemann reports the species in the Normanskill shale at one locality near Lansingburg, New York, and from the Stringtown shale in Oklahoma. Graptolite Faunas, Marathon Region GLYPTOGRAPTUS TERETIUSCULUS nr. SICCATUS (Ellee and Wood) Diplograptus ( Glyptograptus) teretiusculus var. siccatw Elles and Wood, 1907, Mon. British Grapt., p. 253, text figs. 173a, b, pl. 31, figs. 3a-d. Remarks.-The Texas specimens agree closely with the specific description by Elles and Wood. Horizon.-Specimens of this variety were collected from one locality (collection 139) which is in the lower part of the Woods Hollow shale, zone 11. Elles and Wood state that the form is fairly common in the Glenkiln shales and their equivalents in the British Isles. It occurs associated with N emagraptus gracilis and Dicello­graptus sextans in both the Marathon and British sequences. Genue ORTHOGRAPTUS Lapwortb, 1873 ORTHOGRAPTUS CALCARATUS (Lapwortb)? Pl. 18, fig. 9 Remarks.-The rhabdosomes of the Texas specimens referred to this species are all broken. The longest fragment is 6 cm in length and is 3.0 mm in width. The specimens agree in size with Elles and Wood's (1907, Mon. British Grapt., pp. 239-241, text figs. 159a-c, pl. 30, figs. la-c) description of the species. They also agree with the description of 0. calcaratus in character of the thecae, in number of the thecae (8 to 9 in 10 mm) , and in the presence of a stout virgula tube. However, the proximal ends of the Texas specimens are not preserved, and since this is a char· acteristic portion of the rhabdosome of 0. calcaratus, specific identification cannot be made without seeing it. Horizon.-The specimens provisionally referred to 0. calcaratus were collected from the middle part of the Maravillas chert, zone 14 (collections 83A, 131, and 131A). Ruedemann reports the species from the shale at Fall Creek, Hailey quad­rangle, Idaho. Elles and Wood state that "O. calcaratus is a common fossil in the lower Hartfell shales in the zone of DU:ranograptus clingani." Thomas and Keble ( 1933) list the species as present in the Eastonian and Bolindian series of the Upper Ordovician in Victoria, Australia. ORTHOGRAPTUS CALCARATUS var. ACUTUS (Lapwortb) Pl. 16, figs. 3, 4 Diplograptus (Orthograptus) calcaratus var. acutus Lapworth, MS, 1890. Diplograptus (Orthograptus) calcaratus var. acutus Elles and Wood, 1907, Mon. British Grapt., p. 242, text fig. 161, pl. 30, figs. 3a·c. Diplograptus (Orthograptus) calcaratus var. acutus Ruedemann, 1947, Geo!. Soc. America Mem. 19, p. 399, pl. 68, figs. 14-19. Remarks.-The Texas specimens agree fully with the specific description by Elles and Wood. Horizon.-Specimens of this variety were collected from the upper part of the Woods Hollow shale, zone 12 (collections 87 and 94A). Ruedemann states that it is common in the Normanskill shale in New York and that it is also found in the "Athens shale" in Virginia. Elles and Wood record it from the Glen kiln shales in Scotland and Wales. The form occurs with the same associates (Diplograptus multidens and Dicellograptus sextans) in both the British and Marathon successions. Thomas and Keble ( 1933) list the variety acutus from the Eastonian and Bolindian series of the Upper Ordovician in Victoria, Australia. The form apparently appears in younger beds in the Australia sequence than it does in the British Isles or in the Marathon region. ORTHOGRAPTUS CALCARATUS var. ALABAMENSIS (Ruedemann) Diplograptus foliaceus var. alabamensis Ruede­ mann, 1908, New York State Mus. Mem. 11, p. 352, pl. 25, fig. 3. Diplograptus (Orthograptus) calcaratus var. alabamensis Ruedemann, 1947, Geol. Soc. America Mem. 19, p. 399, pl. 68, fig. 20. Remarks.-The Texas specimens agree closely with Ruedemann's description. Horizon.-Specimens of this variety were collected from the upper part of the Woods Hollow shale, zone 12 (collections 94A, 100, and 127). Ruedemann's types came from the Athens shale at Pratts Ferry, Bibb County, Alabama. Decker ( 1952) records the species from several Bureau of Ecorwmic Geology, The University of Texas localities in Alabama, Virginia, and Ten­nessee. ORTHOGRAPTUS cf. 0. CALCARATUS var. BASILJCUS (Lapworth) Pl. 19, fig. 3 Remarks.-The rhabdosomes of the Texas specimens are broken, but they agree in general form with the description by Elles and Wood (1907, Mon. British Grapt., p. 243, text figs. 162a, b, pl. 30, figs. 2a-d). The largest fragment of the Texas material measures 6 cm in length and 2.5 mm in breadth. The thecae number 10 to 12 in 10 mm, overlap one-half their extent, and have an average length of about 3 mm. The Texas specimens agree closely in size and shape and in number and character of the thecae with the descrip­tion of 0. cmcaratus var. basilicus by Elles and Wood. However, in none of the Texas specimens are the proximal ends of the rhabdosomes preserved, and since the nature of the proximal end is a charac­teristic portion of the rhabdosome, specific identification is uncertain. Horizon.-The specimens tentatively re­ferred to 0. cmcaratus var. basilicus were collected from the middle part of the Mara­villas chert, zone 14 (collections 54 and 83A). Elles and Wood state that the variety basilicus "occurs in fair abundance in the zones of Dicranograptus clingani and Pleurograptus linearis" of the Hartfell shales in Scotland and Wales. Thomas and Keble (1933) record the variety from the Eastonian and Bolindian series of the Upper Ordovician in Victoria, Australia. ORTHOGRAPTUS CALCARATUS var. INCISUS (Lapworth) Pl. 17, figs. 3, 7 Graptolithus pristis Hall, 1847, Paleontology of .New York, vol. 1, p. 72, fig. 11. Diplograptus foliaceus var. incisus Lapworth in Ruedemann, 1908, New York State Mus. Mem. 11, pp. 347-349, text figs. 283-287, pl. 24, figs. 1-8. Diplograptus (Orthograptus) calcaratus var. in­ cisus Ruedemann, 1947, Geol. Soc. America Mem. 19, p. 400, pl. 68, figs. 1-13, 24. Remarks.-The Texas specimens are poorly preserved but agree with the de­scription of this variety by Ruedemann in size (up to 4.5 cm in length and 3 mm in breadth), in number of thecae (8 to 9 in 10 mm), in inclination of the thecae ( 40 to 50 degrees to the nemacaulus), in character of the thecae, and in general shape of the rhabdosome. Horizon.-Specimens of this variety were collected from the lower part of the Mara villas chert, zone 13 (collections 106 and 128). Ruedemann reports that this variety is common in the Normanskill shale in New York. The writer has observed it at the New York State Museum at Albany, New York, in collections from the Magog shale and at the University of Oklahoma in collections from the Stringtown shale of Oklahoma and the Womble shale of Ar­kansas. ORTHOGRAPTUS ef. 0. CALCARATUS var. VULGATUS (Lapworth) Pl. 18, fig. 8 Remarks.-The Texas specimens agree with the description of this variety by Elles and Wood (1907, Mon. British Grapt., pp. 241-242, text figs. 160a-c, pl. 30, figs. 5a-d) in size, in the abrupt widening and general coarseness of the rhabdosome, and in the more everted character of the aper­tural margin of the thecae in subsclariform view. However, the thecae are rather sparse (8 in 10 mm compared to 8 to 10 in 10 mm in the British specimens), and the proximal ends are not preserved. Since the nature of the proximal end of the rhabdosome in this variety is an important characteristic, the Texas specimens can be referred to this species only tentatively. Horizon.-Specimens referred to 0. cal,­caratus var. vulgatus were collected from the lower and middle parts of the Mara­villas chert, zone 13 (collections 134 and 134A) and zone 14 (collections 45 and 131A). Ruedemann (1947) records the variety vulgatus from the Magog shale in Quebec. Elles and Wood state that it is an abundant fossil in the lower part of the Hartfell shales of southern Scotland where it occurs in the zones of Climacograptus wilsoni and Dicranograptus clingani. The Texas forms occur in zone 13 of the Mara­ Graptolite Faunas, Marathon Region thon sequence with the same associates (Dicranograptus nicholsoni and Ortho­graptus truncatus var. intermedius) as does the variety 0. calcaratus var. vulga­tus in the zone of Climacograptus wilsoni in Scotland. The form ranges into the next higher zone in both the Marathon and British sequences. Thomas and Keble (1933) list 0. calcaratus var. vulgatus from the Gisbornian and Eastonian series of the Upper Ordovician in Victoria, Aus­tralia. ORTBOGRAPTUS QUADRIMUCRO!'\ATUS (Ball) Pl. 18, fig. 1 Graptolithus quadrimucronatus Hall, 1865, Cana­dian Organic Remains, p. 144, pl. 13, figs. 1-10. Diplograptus (Orthograptus) quadrimucronatus Elles and Wood, 190i, Mon. British Grapt., pp. 223-224, text figs. 145a-f, pl. 28, figs. la-d. Glossograptus quadrimucronatus Ruedemann, 1947, Geol. Soc. America Mem. 19, pp. 452­454, pl. 78, figs. 1-5, not pl. 81, figs. 29-32. Remarks.-The Texas specimens agree closely with the specific description by Elles and Wood. The rhabdosomes of this species do not have the long dorsal and lateral spines which characterize the genus Glossograptus, and the writer follows Elles and Wood in considering it to be an ortho­graptid in which the thecae are nearly rec­tangular in section and the apertural margins are slightly lobate and spinose. Horizon.-Specimens of 0. quadrimn­cronatns were first recognized in collections from the Marathon region by Ruedemann (in Sellards, 1933) . The writer found the species to be a common form in the middle part of the Mara villas chert, zone 14 (col­lections 45, 55, 73A, 83A, and 83B). The species is a characteristic element of the fauna of zone 14 and gives its name to that zone. Ruedemann records the typical form of 0. quadrimucronatus from the Atwater Creek shale in New York and from the Gloucester shale at Lake St. John in the Province of Quebec. Elles and Wood report the species to be a rather common form in the zone of Pleurograptus linearis in the Hartfell shales of southern Scotland. Harris and Thomas (1938b) report that 0. quad· rimucronatus is a common form in the basal part of the Bolindian series (zone of Pleurograptus) of the Upper Ordovician in Victoria, Australia. ORTHOGRAPTUS QUADRIMUCRONATUS var. ANGUSTUS (Ruedemann) Pl. 17, figs. lOa, 11 Glossograptus quadrimucronatus var. angustus Ruedemann, 1947, Geo!. Soc. America Mem. 19, p. 454, pl. 79, figs. 20-24. Remarks.-Ruedemann's types of this slender variety came from the Maravillas chert in the Marathon region. Specimens collected by the writer are identical to those described by Ruedemann. Horizon.-The writer found this variety of 0. quadrimucronatus to be a common form in the lower part of the Maravillas chert, zone 13 (collections 73, 86B, and 134A). ORTBOGRAPTUS QUADRIMUCRONATUS var. CORNUTUS (Ruedemann) Glossograptus quadrimucronatus var. cornutus Ruedemann, 1908, New York State Mus. Mem. 11, pp. 393-394, text figs. 338-342, pl. 27, figs. 8-10. Glossograptus quadrimucronatus var. cornutus Ruedemann, 1947, Geol. Soc. America Mem. 19, p. 455, pl. 78, figs. 23-31. Remarks.-The Texas specimens agree closely with Ruedemann's description of this variety. H orizon.-Specimens of this variety were collected from one locality (collection 134A) which is in the lower part of the Maravillas chert, zone 13. Ruedemann re­cords the species from the Canajoharie shale near Albany, New York, and from the upper part of the Womble shale near Crystal Springs, Arkansas. ORTHOGRAPTUS af'£. 0. TRUNCATUS (Lapworth) Remarks.-The Texas specimens are poorly preserved and broken, so that the nature of the proximal end is difficult to see. However, the fragments of the rhabdo­somes are up to 3 cm in length and 3 to 3.5 mm in breadth; they agree in size with the British material. Also, the thecae agree in number and in character with those of 0. truncatus described by Elles and Wood (1907, Mon. British Grapt., pp. 233-235, text figs. 154a, b, pl. 29, figs. 3a-e) . At the New York State Museum, the writer has Bureau of Economic Geology, The University of Texas examined specimens which Ruedemann identified as Amplexograptus amplexi· caulis and is of the opinion that all of them belong to the Orthograptus truncatus group. Most of the specimens should properly be referred to 0. truncatus itself, but some belong to a distinct variety. Horizon.-The specimens referred to 0. truncatus were collected from the lower and middle parts of the Maravillas chert, zones 13 (collections 86B, 128, and 134) and 14 (collection 83A). Ruedemann (1947) records Amplexograptus amplexi­caulis from the Maravillas chert, the Tren­ton limestone at Trenton Falls near Middle­ville, New York, the Snake Hill shale in New York, and the Viola limestone in Oklahoma. Elles and Wood state that 0. truncatus is an abundant fossil in the zones of Dicranograptus clingani and Pleura· graptus linearis of the Hartfell shales in the British Isles. Thomas and Keble (1933) list 0. truncatus from the Easto· nian and Bolindian series of the Upper Ordovician in Victoria, Australia. ORTHOGRAPTUS TRUNCATUS var. ABBREVIATUS (Elles and Wood) ! Pl. 20, fig. 10 Remarks.-The Texas specimens are small and poorly preserved. The largest specimen is 9 mm in length and widens gradually to a width of 2 mm. The figures of the English types measure 2 mm in width 9 mm from the sicula. The thecae are like those of 0. truncatus but widen conspicuously towards the aperture. In this respect they agree with Elles and Wood's description (1907, Mon. British Grapt., pp. 235-236, text figs. 155a-d, pl. 29, figs. 6a-e). However, the thecae appear to be in­ clined at a slightly higher angle to the stipe than in the English material, but this may be a matter of preservation. Further, the preservation is so poor that the details of the proximal end are obscure. Horizon.-The specimens referred to this variety were collected from the highest beds of the Maravillas chert, zone 15 (col· lection 147). Elles and Wood report the variety to be characteristic of the highest beds of the Hartfell shales (zones of Di­cellograptus complanatus and D. anceps) in the British Isles. The variety occurs with the same associates (D. complanatus and 0. truncatus var. socialis) in both the Marathon and British sequences. ORTHOGRAPTUS TRUNCATUS var. INTERMEDIUS (Elles and Wood) Pl. 17, figs. 4, 5 Diplograptus (Orthograptus) truncatus var. in­ termedius Elles and Wood, 1907, Mon. British Grapt., p. 236, text figs. 156a, b, pl. 29, figs. 4a-e. Remarks.-Some of the Texas specimens agree closely with Elles and Wood's de­scription of this variety except that the thecae number 10 to 11 in 10 mm whereas Elles and Wood give a measure of 10 to 14 in 10 mm. Others of the Texas forms agree with Elles and Wood's description in size and in general form of the thecae, but they do not agree in number of thecae ( 8 to 9 in 10 mm) nor in the overlap of the thecae. These latter forms have been identi· fied as 0. truncatus cf. var. intermedius. Some of the specimens at the New York State Museum which were identified by Ruedemann as Amplexograptus amplexi­caulis should, in the writer's opinion, be referred to 0. truncatus var. intermedius, because these forms agree well with Elles and Wood's varietal description. Horizon.-All specimens of this variety (including those referred to it) were col­lected from zone 13 which encompasses the lower part of the Maravillas chert. The form is a characteristic element of the fauna of zone 13. Good specimens of the variety were identified in collections 73, 86B, and 134A, and specimens referred to the variety were identified in collection 134. Ruedemann (1947) reports the variety from the McKenzie Mountains, North West Territory, Canada. Ruede­mann's specimens identified as A. amplexi­caulis, but which are 0. trur.catus var. intermedius, came from the Trenton lime­stone at Trenton Falls near Middleville, New York, and from the Snake Hill shale in New York. Elles and Wood state that "var. intermedius is especially char· Graptolite Faunas, Marathon Region acteristic of the zone of Climacograptus wilsoni, and also occurs in the zone of Dicranograptus clingani" in the British Isles. Thomas and Keble (1933) list the var. intermedius from the Eastonian and Bolindian series of the Upper Ordovician in Victoria, Australia. ORTHOGRAPTUS TRUNCATUS var, PERTENUIS (Ruedemann) Diplograptus amplexicaulis var. pertenuis Ruede­ mann, 1908, New York State Mus. Mem. 11, pp. 365-366, text figs. 30~310, pl. 25, figs. 14-16. Diplograptus ( Amplexograptus) amplexicaulis var. pertenuis Ruedemann, 1947, Geo!. Soc. America Mem. 19, p. 412, pl. 70, figs. 16-22. Remarks.-The Texas specimens agree closely with Ruedemann's description of the variety pertenuis. The writer has studied the type specimens of this variety at the New York State Museum and is of the opinion that it belongs to the Ortho­graptus truncatus group. Since it belongs to that group, but does not agree with any of the previously described varieties, it is herein considered to be another variety of 0. truncatus. Horizon.-Ruedemann (in Sellards, 1933) first reported the variety pertenuis from the Maravillas chert, and the writer collected it from the lower and middle parts of that formation, zones 13 (collec­tion 134A) and 14 {collection 132) . Ruedemann's type material came from the Snake Hill shale in New York. ORTHOGRAPTUS TRUNCATUS var. RECURRENS (Ruedemann) Pl. 18, figs. 4, 5 Diplograptus recurrens Ruedemann, 1925, New York State Mus. Bull. 262, pp. 5~59, text figs. 42-46, pl. 7, figs. 2-4. Diplograptus ( Amplexograptus) recurrens Ruede­ mann, 1947, Geo!. Soc. America Mem. 19, p. 414, pl. 70, figs. 40--50, 55. Remarks.-The Texas specimens agree closely with Ruedemann's description. The writer has studied the type specimens of this form at the New York State Museum and is of the opinion that it belongs to the Orthograptus truncatus group. The form is close to the variety pauperatus but may be distinguished from it by the closer arrange­ment of the thecae and the smaller dimen­sions of the rhabdosome. The thecae num­ber 13 to 16 in 10 mm in the variety recur­rens and 12 to 14 in the variety pauperatus. Further, the rhabdosome of the variety re­currens is a maximum of 1.8 mm in width and 2.5 cm in length while the rhabdo­some of the variety pauperatus measures a maximum of 2.0 mm in width and 6 cm in length. Because the variety recurrens is different from any previously described variety of 0. truncatus, the writer considers it a distinct variety. Horizon.-Specimens of this variety were collected from the middle part of the Maravillas chert, zone 14 (collections 45, 131A, and 132). Ruedemann records the form from the lower part of the Lorraine group (Whetstone Gulf formation) in New York and from the upper part of the Viola limestone in Oklahoma. ORTHOGRAPTUS TRUNCATUS var. SOCIALIS (Lapworth) Pl. 20, figs. 4-6. Diplograptus socialis Lapworth, 1880, Ann. Mag. Nat. Hist., ser. 5, vol. 5, p. 166, pl. 4, figs. 13a-e. Diplograptus (Orthograptus) truncatus var. so­cialis Elles and Wood, 1907, Mon. British Grapt., pp. 237...:238, text figs. 157a-d, pl. 29, figs. 7a-e. Remarks.-The Texas specimens are not well preserved but appear to agree with Elles and Wood's figures and description of this variety. The form described by Ruedemann (194.7, p. 402, pl. 69, figs. 9-11) as Diplograptus (Orthograptus) nexus is an Orthograptus of tht truncatus type and is quite similar to the variety socialis. Horizon.-Specimens of this variety were collected from the highest beds in the Maravillas chert, zone 15 (collection 60). Elles and Wood report it to be common in the zone of Dicellograptus complanatus in the upper part of the Hartfell shales in the British Isles. ORTHOGRAPTUS WHITFIELDI (Hall) Pl. 16, fig. 7 Graptolithus whitfieldi Hall, 1859, Paleontology of New York, vol. 3, p. 516, fig. 1. Bureau of Economic Geology, The University of Texas Diplograptus (Orthograptus) whitfieldi Elles and Wood, 1907, Mon. British Grapt., pp. 227-228, text figs. 149a, b, pl. 28, figs. 6a-d. Glossograptus whitfieldi Ruedemann, 1947, Geol. Soc. America Mem. 19, pp. 457-458, pl. 77, figs. 23-26. Remarks.-The Texas specimens agree well with the specific description by Elles and Wood. The rhabdosomes of this species do not have the long dorsal and lateral spines which characterize the genus Glosso­graptus, and the writer follows Elles and Wood in considering it to be an ortho­graptid in which the thecae are nearly rec­tangular in section and the apertural mar­gins are slightly lobate and spinose. Horizon.-Specimens of 0. whitfieldi were collected from the upper part of the Woods Hollow shale, zone 12 (collections 94A, 105, and 127). Ruedemann records the species from the Normanskill shale in New York and from the Womble shale in Arkansas. Elles and Wood report it from the Glenkiln shales in the British Isles. It occurs in both continents with the same associates (Diplograptus multidens, Dicel­lograptus sextans, and Climacograptus bi­cornis). Family ?DIPLOGRAPTIDAE lncertae Sedis Genus TRIGONOGRAPTUS Nicholson, 1869 TRIGONOGRAPTUS ENSIFORMIS (Hall) PL 12, fig. 10; PL 13, figs. 6, 7 Graptholithus ensif ormis Hall, 1858, Canada Geol. Survey, Rept. Prog. for 1857, p. 133. Trigonograptus ensiformis Elles and Wood, 1908, Mon. British Grapt., pp. 302-303, text figs. 202a-c, pl. 35, figs. la-c. Trigonograptus ensiformis Ruedemann, 1947, Geol. Soc. America Mem. 19, pp. 447-448, pl. 76, figs. 49-57. Remarks.-The rhabdosomes of the Texas specimens are smaller than the type forms in length and width but agree in all other details. The length of the Texas speci­mens ranges from 2 to 5 cm, with an aver­age of about 3 cm, and the width ranges from 1.5 to 3 mm, with an average of about 2 mm. The thecae number 9 to 11 in 10 mm, are inclined at an angle of 45 degrees, and are in contact throughout their length. Horizon.-T. ensiformis is common in the upper part of the Fort Peiia formation, zone 9 (collections 13, 15, 28, and 98) . A few specimens were found in the lower part of that formation, zone 8 (collection 62). The species is common in zone 3 (zone of Diplograptus dentatus) of the Deepkill shale in New York. Hall's types came from the Levis shale in Quebec, and Raymond (1914) lists it from his zone D (zone of D. dentatus) of that formation. Elles and Wood record T. ensiformis from the upper part of the Skiddaw slates in the British Isles, and Harris (1935) records it from the lower two zones of the Middle Ordovician in Victoria, Australia. Family LASIOGRAPTIDAE Bulman, 1955 Genus HALLOGRAPTUS Lapworth, 1877 HALLOGRAPTUS BIMUCRONATUS (Nicholson) Diplograptus bimucronatus Nicholson, 1869, Ann. Mag. Nat. Hist., ser. 4, vol. 4, p. 236, pl. 11, fig. 12. Lasiograptus (Hallograptus) mucronatus var. bimucronatus Elles and Wood, 1908, Mon. British Grapt., pp. 323-324, text figs. 212a, b, pl. 33, figs. 8a-e. Lasiograptus (Hallograptus) bimucronatus Rue­demann, 1947, Geol. Soc. America Mem. 19, p. 465, pl. 80, fig. 52, pl. 81, figs. 11-28. Remarks.-This distinctive form was originally described by Nicholson as a dis­tinct species, but Elles and Wood included it as a variety under Lasiograptus (Hallo­graptus} mucronatus. The writer is of the opinion that the differences are sufficient to distinguish the two forms as separate species. H. bimucronatus has closely set thecae (12 to 16 in 10 mm) whereas H. mucronatus has 8 to 10 thecae in 10 mm. The rhabdosomes of H. bimucronatus are medium sized, attaining a length of 5 cm or more, although specimens attaining a length of 3 cm are of most frequent occur­rence. Mature forms are 3 mm wide. This width is attained 15 mm from the sicula. Rhabdosomes of H. bimucronatus are wider and longer than those of H. mucro· natus. Further, the apertural spines in H. bimucronatus are thick~r and diverge earlier than those of H. mucronatus so that the paired nature of the spines is nearly always seen, and some specimens of H. bimucronatus show distinct scopulate processes extending outward beyond the margin of the thecae. The Texas speci· Graptolite Faunas, Marathon Region mens of H. bimucronatus agree in all re· spects with the description by Ruedemann of Lasiograptus (H allograptus) bimucro­natus. Horizon.-H. bimucronatus was col­lected from the Woods Hollow shale, zones 11 (collection 137) and 12 (collection 94B). Ruedemann records the species from the Normanskill shale in New York and the Womble shale in Arkansas. Elles an di Wood state that this form is fairly common in the zone of Nemagraptus gracilis of the Glenkiln shales in the British Isles. The species occurs with identical zonal assemblages in the British and Marathon successions. HALLOGRAPTUS ECHINATUS (Ruedemann) Glossograptus echinatus Ruedemann, 1904, New York State Mus. Mem. 7, pp. 725-726, text fig. 102, pl. 16, figs. 30--32. Lasiograptus (Hallograptus) echinatus Ruede­ mann, 1947, Geol. Soc. America Mem. 19, pp. 462-463, pl. 77, figs. 9-12, 14, not figs. 13, 16. Remarks.-The Texas specimens agree well with Ruedemann's specific descrip­ tion. The genus of this form is in some doubt, but the writer follows Ruedemann's last opinion and leaves the form in the genus Hallograptus. Bulman (1955) raised Hallograptus from subgeneric to generic status. The form from the Glenogle shale (fig. 13) is not the same species as the New York and Marathon forms. Horizon.-This species was collected from zone 9, the upper part of the Fort Pena formation (collections 13, 42, 98, and 149). Ruedemann (in Sellards, 1933) first identified the species from the Mara­ thon region, and his type material came from the Diplograptus dentatus zone of the Decpkill shale in New York. HALLOGRAPTUS ETHERIDGEI (Harris) Pl. 12, figs. 6, 9b; Pl. 13, fig. 4 Lasiograptus (Thysanograptus) etheridgei Harris, 1924, Royal Soc. Victoria, Proc. (n.s.), vol. 36, pp. 98--99, pl. 7, figs. 3-7. Remarks.-The Texas specimens agree well with Harris' specific description ex­cept that the Texas specimens have a maxi­mum width of 3 mm (exclusive of the ex­ ternal meshwork), while Harris records a maximum width of 4 mm. H. etheridgei resembles the British L. costatus but the British form has more closely set thecae (10 to 16 in 10 mm) and the main ribs of the meshwork originate from the mesial angles of the thecae and curve outward, then downward. The thecae number 9 to 11 in 10 mm in H. etheridgei, and the main ribs of the meshwork appear to arise from the aperture of the thecae and curve out­ward, then split with one part curving downward and the other curving upward. The main ribs of H. etheridgei are thicker than in the British form, and frequently the rhabdosomes and only the main ribs of the mesh are preserved and those ribs show the split at their distal end. The sicula is about 1 mm in length and in some speci­mens the virgella appears to be thickened and projects downward for 1 mm from the sicula. Theca 11 grows downward for the greater part of its length then bends up­ward in the region of the aperture and Th 12 appears to grow downward at first be­fore bending upward; the proximal end has a cryptograptid aspect. Horizon.-H. etheridgei is a common form in the upper part of the Fort Peiia formation, zone 9 (collections 13, 14, 15, 117, and 149) and has been selected as the name-giving species of that zone. Harris (1935) lists it as very common in the zone of Glyptograptus intersitus of the Middle Ordovician of Victoria, Australia. The species occurs with the same associates (Trigonograptus ensiformis, Glyptograptus intersitus, and Cryptograptus schaferi) in both the Marathon and Victorian se­quences. HALLOGRAPTUS MUCRONATUS (Hall) Pl. 16, fig. 6 Graptolithus mucronatus Hall, 1847, Paleontology of New York, vol. 1, p. 268, pl. 73, figs. la-d. Lasiograptus (Hallograptus) mucronatus Elles and Wood, 1908, Mon. British Grapt., pp. 321­322, text fi gs. 210a, b, pl. 33, fi gs. 6a-e. Lasiograptus ( H allograptus) mucronatus Ruede­mann, 1947, Geo!. Soc. America Mem. 19, pp. 463-464, pl. 81, figs. 1-9. Bureau of Economic Geology, The University of Texas Remarks.-The Texas specimens agree fully with the specific description by Ruedemann. Horizon.-Only a few specimens of this species were found, and they came from the upper part of the Woods Hollow shale, zone 12 (collections 87, 94A, and 94B). It is one of the commonest forms in the Nor­manskill shale in New York. Decker (1952) lists it from the Stringtown shale of Oklahoma and the Womble shale of Arkansas. Elles and Wood described it from the Glenkiln shales of Scotland, Wales, and Ireland. The forms listed as Lasiograptus (H allograptus) etheridgei Harris from Victoria, Australia, are dis­tinct species and are not synonymous with Hallograptus mucronatus as Ruedemann (1947) suggested. Family RETIOLITIDAE Lapworth, 1873 Subfamily ARCHIRETIOLITINAE Bulman, 1955 Genus RETIOGRAPTUS Hall, 1859 RETIOGRAPTUS DECKERI Ruedemann Retiograptus sp. Decker, 1935, Jour. Paleont., vol. 9, p. 708, fig. 21. Retiograptus deckeri Ruedemann, 1947, Geol. Soc. America Mem. 19, pp. 458-459, pl. 80, figs. 33-41. Remarks.-The Texas specimens are small but agree well with Ruedemann's specific description. Horizon.-Specimens of R. deckeri were collected from the top of the Maravillas chert, zone 15 (collection 60). Ruedemann records the species from both the Polk Creek shale in Arkansas and the Sylvan shale in Oklahoma. RETIOGRAPTUS GEINITZIANUS Hall PI. 15, fig. 3a Retiograptus geinitzianus Hall, 1859, Paleon­ tology of New York, vol. 3, p. 518. Retiograptus geinitzianus Elles and Wood, 1908, Mon. British Grapt., pp. 316-317, text figs. 209a-c, pl. 34, figs. 7a-d. Retiograptus geinitzianus Ruedemann, 1947. Geol. Soc. America Mem. 19, pp. 459-460, pl. 80, figs. 11-26. Remarks.-The Texas specimens agree well with the specific description by Elles and Wood. Many of the specimens are fragmentary, but some whole rhabdosomes were found. Horizon.-Fragments of this species are common in zones 11 and 12 (collections 94A, 122, 136, 137, and 139) and are common elements of the fauna of the Woods Hollow shale. Hall's types came from the Normanskill shale at Albany, New York, and the species has been re­corded by Ruedemann from several other localities in the Normanskill shale. Ruede­mann also reports it from the Womble shale in Arkansas, the "Athens" shale at Pratts Ferry, Alabama, and the Glenogle shale in British Columbia. Elles and Wood state that "R. geinitzianus is a rare fossil in the Glenkiln shales" of Scotland and Wales, and T. S. Hall (1920) listed the species from the Upper Ordovician of Vic­toria, Australia. The species is found with the same associates (Nemagraptus gracilis, Dicellograptus sextans, Climacograptus antiquus) in North America, England, and Australia. RETIOGRAPTUS PULCHERRIMUS Keble and Harris Pl. 17, figs. 9, lOb Retiograptus pulcherrimus Keble and Harris, 1934, Nat. Mus. Melbourne Mem. 8, pp. 178­ 179, text fig. 6, pl. 22, fig. 1. Remarks.-The Texas specimens agree fully with the specific description by Keble and Harris. Horizon.-This species is a common form in the lower and middle parts of the Maravillas chert, zones 13 and 14 ( collec­tions 45, 55, 73, 83B, 86B, 132, 134, and 134A). Harris and Thomas (1938b) state that it is part of a distinct assemblage in the highest zone of the Upper Ordovician, Bolindian series in Victoria, Australia. The species occurs lower in the Marathon suc­cession than it does in the Victorian. RETIOGRAPTUS SPECIOSUS Harris? Remarks.-The Texas specimens are poorly preserved, many are broken or bent, but they appear to agree with the descrip­tion by Harris (1924, Royal Soc. Victoria, Proc. (n. s.), vol. 36, pp. 99-100, pl. 8, Graptolite Faunas, Marathon Region figs. 8-10). The test has not been preserved in any of the specimens so that the clathria can be clearly seen. Horizon.-The Texas specimens were collected from one locality (collection 13) which is in the upper part of the Fort Pena formation, zone 9. Harris and Thomas ( 1938b) figure R. speciosus as a common form in the Middle Ordovician in Victoria, Australia. RETIOGRAPTUS TENTACULATUS (Hall)? Remarks.-The Texas specimens are poorly preserved but appear to agree with the specific description by Ruedemann (1947, Geol. Soc. America Mem. 19, pp. 460-461, pl. 80, figs. 1-5, not figs. 6-10), except that the width is slightlv less (3.5 mm whereas the New York material is 4.0 mm). The forms from the GlePogle shale (figs. 6-10) which Ruedemann included in this species are larger than the New York, Arkansas, and Texas forms, and they possess lacinia. They are a species distinct from R. tentaculatus and should probably be referred to Hallograptus etheridgei. Because the Texas specimens are poorly preserved and are slightly nar­rower than the types, the writer refers them provisionally to Hall's species. Horizon.-The specimens tentatively re­ferred to R. tentaculatus were collected from one locality (collection 98) which is in the upper part of the Fort Pena forma­tion, zone 9. Hall's types came from the horizon with Diplograptus dentatus (Ray­mond's zone D) of the Levis shale in Que­bec. Ruedemann records the species from the beds with Diplograpt'us dentatus in the Deepkill shale in New York and from the Glenogle shale in British Columbia. BIBLIOGRAPHY ABERDEEN, ESTHER (1940) Radiolarian fauna of the Caballos formation, Marathon basin, Texas: four. Paleont., vol. 14, pp. 127-139. ADAMS, J. E., et al. (1952) Marathon basin, Brewster and Pecos counties, Trans-Pecos Texas: West Texas Geo!. Society Guidebook. ARKELL, W. J. (1956) Comments on stratigraphic procedure and terminology: Amer. Jour. Sci., vol. 254, pp. 457-467. BAKER, C. L., and BowMAN, W. F. (1917) Geo­logic exploration of the southeastern Front Range of Trans-Pecos Texas: Univ. Texas Bull. 1753, pp. 67-172. BARRASS, R. (1954) Graptolites from Anticosti Island: Geo!. Soc. London Quart. Jour., vol. llO, pp. 55--75. BARTON, J.M. (1945) Pre-Permian axes of maxi­mum deposition in west Texas: Bull. Amer. 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(1901) Hudson River beds near Albany and their taxonomic equivalents: New York State Mus. Bull. 42, pp. t of Marathon. The line of bearing of the section is S. 55° E. THICKNESS Feet Inches A.lsate shale-­Shale, black, breaks into rhomboid chips 46 Marathon limestone-­ [ pper part of Marathon limestone-­Conglomerate. composed of fiat chips and slabs of limestone .................... ........ . 5 Limestone. gray. fine grained. thin bedded. cross laminated. in layers .t to 6 inches thick interbedded with dark gray. sublithographic limestone which weathers bluish gray in layers 2 to 3 inches thick ..................... .............. 25 Limestone. dark gray. sublithographic. weathers bluish gray. COLLECTION 30: Did,mograptu.s protobi/idus. Ph,·Uograptu.s ilicifoliu..s, PhyUograptus angu.sti­folius, Tetragraptus quadribrachiatus .. .. ...... ..... . . .. ...... ... .... . 6 Limestone. dark gray. sublithographic. weathers bluish gray in layers 6 to 8 inches thick interbedded with thin-bedded. cross-bedded. gray, fine-grained limestone in layers .t to 6 inches thick. COLLECTIO:o< 5, from 12 feet above base of this part of the section: Dic~·onema sp., Didymograptu.s sp . ..... .. ... .. ...... . 118 Conglomerate. composed of fiat limestone slabs which are elongate subparallel to the bedding l Bureau of Economic Geology, The University of Texas THICKNESS Feet Inches Limestone, dark gray, sublithographic, weathers bluish gray, in layers 4 to 6 inches thick interbedded with thin-bedded, fine-grained, gray limestone in layers 3 to 6 inches thick --­----------------­--------------­---­--··----·----····­·-·········--­····­·­· Subgraywacke, coarse grained, weathers brown ·---­·-­-------------·----·­----···--·---­··--·­--·--·--­-­Limestone, dark gray, sublithographic, weathers bluish gray in layers 4 to 6 17 6 inches thick, interbedded with thin-bedded, cross-bedded, gray, fine-grained limestone in layers 6 to 8 inches thick. COLLECTION 4, from 20 feet above the base of this part of the section: Didymograptus extensus, Tetragraptus fruti· cosus (4-branched) ---·­---·---··-········-······-·--····--···--···-----·---·--------·-----·---···­·-·-----------­---·--··· Monument Spring dolomite member­ 85 Limestone, dolomitic, blue and yellowish, fine grained, weathers orange, in oval lenses. Shale and thin-bedded, gray, fine-grained limestone lies around and between the lenses. COLLECTION 31 : A rcheoscyphia sp., fragments of orthoid brachiopods, cephalopods, and gastropods ·----------­---··---·­··---­-··---·-··­ 65 Total upper part of Marathon limestone and Monument Spring dolomite member.... 317 Break section because of complex folding. Lower part of Marathon limestone- Shale, buff, calcareous ________ --­------··---········---···­----­--·---­------­--··---·-·--­---· 18 Conglomerate, composed of flat limestone slabs which are subparallel to the bedding -------· _­----·---··---···--­____ ______ -·-­------­----­---­-··-·---·----·---­Limestone, gray, fine grained, thin bedded, cross laminated, interbedded with 1 dark gray, sublithographic limestone which weathers bluish gray. COLLECTION 3: Acrotretid brachiopods _____ ___ ------·-­-·--·­-----­·---··-·­-----··-·­---···--·--·­ 18 9 Conglomerate, composed of flat chips and slabs of limestone .... -·­---­--·--­---­--___ l Limestone, dark gray, sublithographic, weathers bluish gray, in layers 4 to 6 inches thick interbedded with thin-bedded, cross-laminated, gray, fine-grained limestone in layers 6 to 8 inches thick. COLLECTION 2: Clonograptus flexilis, Clonograptus sp. ___ ---·­__ __ ---··---­--··-----------·---·----­--··--------·­---­------­-·-­Conglomerate, composed of flat limestone slabs which are subparallel to the 42 bedding ··-·-----·····­·····-·--·--····-·····----···-------·---------------·-­-··-------·­----­---------------------­ 16 5 Shale, buff, calcareous ----­--------------·---·----· -·-­---··--·------­-----­----­-·­---­----·----····-·--··--··--·--­------ 28 3 Conglomerate, composed of flat limestone slabs which are up to 2 feet in length and are elongate subparallel to the bedding _ ________ ____ ---·-·--·­-··-···--······-··­ 5 Shale, black, weathers greenish, interbedded with buff, calcareous shale ----·­··­·­-···· 23 4 Shale, buff, calcareous _____________ -----------·-·---·---·--·-·­-·-·--·-----···-· ·-·-···­·---­--·----·-------·· Conglomerate, composed of flat limestone slabs __ ___ ____ --·­__ _________ _ __ _ 46 l 9 6 Limestone, gray, fine grained, thin bedded. COLLECTION l: Lingula sp. ---·----------­ 4 6 Conglomerate, composed of flat limestone slabs which are elongate subparallel to the bedding _ ···----------···­__ --­----­··-·---­______ -·--··--·-··-····-······················-·--· ____________ _ 10 Sandstone, quartzose, coarse grained, weathers brown ·-----··----·­----··-­------·--­----···­········ 4 Shale, buff, calcareous ·-----­-----­--·­-------------·--­-----------­-------------­-------­-·-----­--------­---­--­-----·­_ 5 4 Conglomerate. composed of flat limestone slabs which are elongate subparallel to the bedding ----------------------­---------­-----------·--·-----------·-· -·--·--··-·········--·· Limestone, gray, fine grained, thin bedded __ _____ _ ___ __ __ __ _____ __ ___ _____ _ __ _____ _______ ____ ____ 16 4 6 Conglomerate, composed of flat limestone slabs which are elongate subparallel to the bedding --------------­--------···-­----·-·-·· --········--·····-­-·­·-···-·---·-­---­---­-· --------­------·-·-····· __ Limestone, gray, fine grained, thin bedded, cross laminated, interbedded with 4 dark gray sublithographic limestone which weathers bluish gray _ Conglomerate, composed of flat limestone slabs _____ . .. ____ _...... __.. ___ ______ 57 2 6 Limestone, gray, fine grained, thin bedded, cross laminated, interbedded with dark gray, sublithographic limestone which weathers bluish gray --­---­-----­--------· 21 4 Conglomerate, composed of flat limestone slabs ·-­---········-····---···-----·--····-····· 2 Total lower part of Marathon limestone exposed __________________ 329 6 SECTION IV Section in creek bed on south side of U.S. Highway 90, 1 mile west of railroad station in Marathon. The section was mea~ured in northwest direction. THICKNESS Feet Inches Marathon limestone­Covered. Limestone, dark gray, sublithographic, weathering bluish gray, in layers l to 6 inches thick --------------------··-··-··--··--------····-···--····--·····-····-··-------------------·--·--·--·-·---------------------· 55 Covered ----··-··-·········-·····-··-··-··--·-···········-···---···--·····-·······---········-----------------------------··-------··-····-· 49 Graptolile Faunas, Mar