A small Lower Permian pelvcosaur, Oedaleops n. gen., is known from some skulls and associated dentary bones from the Cutler Formation of Rio Arriba Countv, New Mexico. The new species O. campi is almost certainly an ancestor of the later Eothyris and perhaps Colohomycter, which together with several less well known forms comprise the family Eothyrididae. This family appears to be antecedent to the Caseidae whose basic radiation occurred later than that of the Eothyrididae, and which may represent a fourth pelycosaurian suborder-Caseosauria of Williston. The Eothyrididae provide a route by which the caseid lineage could have passed through the Ophiacodontia from a time as remote as mid-Pennsylvanian. Although Edaphosauria of this age are unknown there is little doubt that the suborder was in existence prior to its first appearance in later Pennsylvanian rocks. Resemblances between edaphosaurs and caseids often noted by authors may have been inherited from similarly ancient ancestors.