Abstract

A new species of Seymouria, S. sanjuanensis, is described on the basis of specimens from the Lower Permian Organ Rock Shale, Cutler Group, San Juan County, Utah. T. E. White has noted that haemal arches begin farther back in the caudal column in the males; othher possible dimorphic differences are that in males the interorbital breadth is less, the maxillary bone is deeper, and the dentition in general and the 'canine' teeth in particular are more prominent. A specimen of Seymouria sp. from the Wichita Group of Texas indicates that two lines of Seymouria, one in the Four Corners area and one in the Midcontinent, may have evolved independently of one another after separation by a barrier to faunal exchange.

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