90 A REVISION OF THE COTYLOSAURIA OF NORTH AMERICA 



the rest of the crown. The apex of this cusp was originally sharp, but seems to 

 have been worn blunt by attrition. The shape of these teeth indicates the assump- 

 tion of an herbivorous habit and perhaps indicates the method of development of the 

 Diadectid teeth. 



"The exact outlines of the frontals, nasals, prefrontals and lachrymals can not 

 be made out; the frontals were paired and took part in the upper edge of the orbit. 



"The jugal is a long and slender bone which underlay the orbit and extended 

 relatively far anterior and posterior to it; it did not extend upward to form a portion 

 of the posterior edge, as in the Pelycosauria. 



"The postorbital region is crushed in both specimens, but in them and in the 

 type specimen it is evident that the region was covered by a complete roof without 

 temporal vacuities. The form of the separate bones is obscure. The quadrate 

 is a vertical plate and the articular surface has two condyles, elongate anteropos- 

 teriorly as in the Dtadectidce. 



"The posterior surface of the skull is composed of a nearly vertical plate in 

 which the sutures are mostly indistinguishable; the exoccipital is fused with the 

 basioccipital and extended well up on the sides of the large and nearly circular 

 foramen magnum. The occipital condyle is slightly oval and is marked by a pit 

 showing the termination of the notochord. The opisthotic is separate from the 

 exoccipital and extends out to the quadrate as a strong process. On either side ot 

 the posterior face of the skull there is a good-sized posttemporal vacuity. There 

 is no trace of a foramen quadratum. 



"The under surface of the skull is most interesting, showing the strong resem- 

 blance to the Captorhinidce in the presence of the strong parasphenoid rostrum and 

 the external process of the pterygoids, points in which it differs from the Dtadectidce. 

 The basisphenoid is shaped much like that in the Pelycosauria and the Captorhinidce; 

 attached to the anterior end is a slender parasphenoid rostrum, which is of excep- 

 tional length; it extended far forward between the palatines. The posterior end is 

 expanded and the lower surface is excavated by a shallow pit; near the anterior end 

 are prominent basipterygoid processes which bear smooth articular faces. There 

 is no trace of foramina for the external carotids on the lower surface, but these may 

 be very obscure because of their minute size and the condition of the surface oi the 

 bone. In the specimen numbered 4685 the basioccipital has been pushed forward 

 out of place and lies partly in the pit at the posterior end of the basisphenoid. 



"The pterygoid has the tripartite form familiar in the Pelycosauria and the 

 Diadectidce. The anterior process extends forward and fuses with the palatine 

 so intimately that the suture can not be made out; between the pterygoids and pala- 

 tines of the two sides there is considerable space which is divided by the elongate 

 parasphenoid rostrum; it is probable that the anterior end of the dividing plate is 

 formed by the vomer. The external process of the pterygoid curves outward from 

 the middle of the bone and presents a prominent vertical face to the inner side of the 

 lower jaw. The lower edge of this process carries a row of prominent, bluntly 

 conical teeth, set in sockets. There are six teeth in the best-preserved row with the 

 base of a seventh set off to one side; the outer end of the row of teeth is bent sharply 

 forward with the process. 



"The lower jaw is very high posteriorly and becomes more slender anteriorly. 

 The alveolar edge is nearly straight, as in the maxillary, and there are 13-14 counted 

 teeth and alveoli; this series does not seem to be complete and there were probably 

 one or two more. As in the upper jaw, there is no trace of enlarged canines and the 

 teeth in the middle of the series are somewhat larger than those at the ends; the 

 last two teeth are abruptly smaller. The teeth of the middle portion of the series 



