_Delorhynchus_ resembles the nitosaurids in size, the shape and sharpness of the teeth, their recurvature and the slight enlargement of their bases, the exclusion of the lacrimal bone from the narial margin (in _Mycterosaurus_) and the apparent lack of a special canine pair of teeth. Resemblances to the caseids are to be noted in the enlargement of the naris (4.5 mm. in height as opposed to 1.7 mm. in _Colobomycter_), lack of development of canines, presence of an infraorbital canal (in _Cotylorhynchus_) and absence of many replacement gaps in the marginal row of teeth. The absence of caniniform enlargement and the extension of the maxilla dorsad of the naris exclude _Delorhynchus_ from the Eothyrididae (Ophiacodontia) but are no bar to its inclusion in the Nitosauridae (Edaphosauria). The marginal teeth of _Delorhynchus_ are simple and primitive, being much like those of the nitosaurids that are described in the literature. The large narial opening and its posterior, dorsal and ventral enclosure by the maxilla, the infraorbital canal, and the sculptured external surfaces of the maxillary fragments indicate that _Delorhynchus_, in these features at least, is close to achieving the caseid grade. Family SPHENACODONTIDAE =Thrausmosaurus serratidens= new genus and new species (_Thrausmosaurus_ is formed from the neuter Greek noun, _thrausma_, meaning fragment, and the masculine Greek noun, _sauros_, meaning reptile. The specific name, _serratidens_, is formed from the Latin _serratus_, meaning serrate, and the masculine Latin noun, _dens_, meaning tooth. The specific name is used as a substantive in apposition with the generic name.) _Type specimen._--Fragmentary left dentary, bearing five teeth, the most posterior of which is broken at the base, KU 11120. _Referred specimens._--Fragmentary ?left maxilla, having two teeth, KU 11121; fragmentary left dentary having two teeth, KU 11122. _Horizon and locality._--From the early Permian fissure deposits in the Arbuckle limestone of the Dolese Brothers Limestone Quarry, approximately 6 miles north of Fort Sill, in sec. 31, T. 4N, R. 11 W, Comanche County, Oklahoma. _Diagnosis._--Small; teeth thecodont, compressed laterally, recurved distally, and bearing anterior and posterior cutting edges; anterior serrations limited to recurved portions of teeth, posterior serrations extending nearly entire length of teeth; lateral compression of teeth more pronounced medially than laterally; bases of teeth expanded. _Description._--The type specimen is 16 mm. long. It bears five teeth that are implanted in a straight row. Empty sockets are present between the first and second teeth, and the third and fourth teeth. The first tooth is 3.0 mm. long, the middle two are each 2.5 mm. long, and the fourth tooth is 2.0 mm. long. The fifth tooth is broken off at its base.