Case and Williston — Description of Reptilian Skulls. 343 



middle portion of the pterygoid widens and is slightly concave 

 on the lower face ; this portion is marked by a low line con- 

 vex anteriorly. On the outer side of the middle of the bone 

 is the low ectopterygoid process : its outer edge and a portion 

 of the upper surface is slightly rugose, but there is no approach 

 to the prominence which the same process gains in Lahido- 

 saurus and Captorhinus and there are no teeth on the process. 

 Near the median vacuity there is slightly prominence on the 

 inner edge of the bone which curves inward and backward 

 over the vacuity. The articulation with the basisphenoid is 

 by, strong flat faces. The pterygoids are separate from the 

 basisphenoids in the specimen, but were found articulated in 

 position so that the nature of the free articulation is beyond 

 doubt. Posteriorly the pterygoids send the usual vertical 

 plates back to join the quadrate. 



There is no evidence of an ectopterygoid. This bone has 

 been in question, but it seems to us there can no longer be 

 donbt of its absence. 



The basisphenoid is represented by the anterior end, only. 

 There is a small but well developed foramen in the middle 

 line. The parasphenoid rostrum is strong ; the lower edge is 

 thick and flat but the upper edge is thin and the whole bone 

 becomes thin anteriorly ; it terminates freely a little beyond 

 the point where the median vacuity is closed by the approxi- 

 mation of the pterygoids or prevomers. It is apparently this 

 bone which was figured by Case as the ethmoid in Diadectes 

 phaseolinus. It is worthy of note that this bone, so strong in 

 this specimen, is wanting in many of the described skulls of 

 Diadectes, perhaps by accident, and it was originally reported 

 that it was absent. 



Above the parasphenoid process there are the shattered 

 remains of very thin plates of bone which can not be restored. 

 It is apparent that they were paired and that they reached up 

 to the lower surface of the parietal or frontal bones. They 

 are probably the anterior ends of the sphenoid plates described 

 by Case. 



The quadrate resembles the same bone in the specimen of 

 Diadectes described by Case from Texas (No. 4839 Am. Mus. 

 Nat. Hist.), but the shaft is a little longer and there is a promi- 

 nent tuberosity on the posterior surface just above the articular 

 surface. It is probable that there was such a tuberosity on 

 the Texas specimen but that it was destroyed by the accidents 

 of fossilization. 



It is necessary here to correct certain errors in the restora- 

 tion of the skull of Diadectes published by Broom (Bull. Am. 

 Mus. Nat. Hist., vol. xxviii, Art. XX, pp. 216-217, figs. 11 

 and 12). In figure 11, the side view, Broom shows an enlarged 

 anterior maxillary tooth resembling a canine, a diastema, 



