Case and Williston — Description of Reptilian Skulls. 347 



length, forming a deep median keel ; there is no median vacuity 

 between the pterygoids but posterior to them there is a deep 

 vacuity, the circular opening of which looks backwards and 

 downwards at an angle of nearly 45° to the horizontal axis of 

 the skull. 



The posterior aspect of the skull. — The occipital portion is 

 narrower than Diadectes owing to the position of the quadrates 

 and the paroccipitals and exoccipitals are shorter. The artic- 

 ular face of the quadrate is much narrower than in Diadectes 

 and the whole bone occupies a very different position with rela- 

 tion to the basicranium. In Diadectes lentus the quadrate lies 

 much farther forward, the articular surface being opposite the 

 posterior end of the basisphenoid ; in Diadectes phaseolinus 

 the articular face of the quadrate lies opposite the middle of 

 the same bone, while in Animasaurus carinatus it lies pos- 

 terior to the posterior end of the bone. This accounts largely 

 for the wider appearance of the posterior end of the skull in 

 the latter. 



The individual bones can not all be made out, but such as 

 can are described below. 



The maxillaries are similar to those of Diadectes except as 

 noted in the description of the palatine process. The posterior 

 end of the bone is continuous w T ith and on the same level as 

 the jugal ; in Diadectes it stands out as prominent point. There 

 are nine bases of teeth and alveoli in the portion of the bone 

 preserved. The posterior one was small and conical, as indi- 

 cated by the base. The others are gradually enlarged until 

 the 6 or 7 from the posterior end is reached, then they begin 

 to diminish in size. There should be two more teeth in the 

 maxillary if the number was the same as in Diadectes. 



The pterygoids have the general form of those in Diadectes; 

 the posterior vertical plate, reaching to the quadrate, is iden- 

 tical in form ; the ectopterygoid process is similar but is more 

 prominent. Laterally the pterygoid joins the maxillary with 

 no indication of an ectopterygoid bone, but the sutures can 

 not be made out. Anterior to the ectopterygoid process the 

 bone widens and dips beneath the matrix, but it is apparent 

 from a break on the left side that it joins the palatine and 

 maxillary as in Diadectes. Just anterior to the ectopterygoid 

 process there is a large shallow pit on the flat surface of the bone 

 but there is no perforation. In fact there is not, in any Ameri- 

 can Permian reptile known to us, any indication of a lateral 

 palatal opening or of a separate ectopterygoid. On the inner 

 side of the bone the posterior portion rises abruptly to form 

 the side of the circular vacuity anterior to the basisphenoid. 

 Immediately in front of this opening the keel formed by the 

 conjoined edges of the pterygoids of the two sides is very high. 



