Structure and Affinities of the Endothiodont Beptiles. 277 



Peisteeodon mackayi, Huxley. 



Pristerodon is closely allied to Opisthoctenodon, but differs in 

 having two well-developed tusks. The only known specimens have 

 been found at East London in beds of probably similar age to those 

 of Pearston and Beaufort West. In Huxley's type, which is now in 

 the British Museum, there is no evidence of tusks, but this is pro- 

 bably due to the imperfection of the specimen. In a specimen sent 

 many years ago to the South African Museum by Mr. G. McKay the 

 tusks are very distinct. In other respects the South African Museum 

 specimen agrees closely with Huxley's type. The whole skull is 

 more strongly built than in Opisthoctenodon. In the middle line of 

 the snout is a prominent median ridge, and there is a parallel ridge 

 above each nostril as in Esoterodon. The mandible is broader and 

 shorter than in Opisthoctenodon, and turns up much more abruptly 

 in front. At the back part of the dentary is a very strong longi- 

 tudinal ridge, which passes directly outwards. There are con- 

 siderably more teeth in the jaw of Pristerodon than in Opistho- 

 ctenodon. In the South African Museum specimen there are at 

 least six in a row. 



Chelyoposaueus williamsi, Broom. 



The type of this species was discovered in a block of sandstone in 

 the Premier Diamond Mine at Kimberley by Mr. Gardner Williams, 

 after whom the specimen has been named. A preliminary descrip- 

 tion was published in the Eecords of the Albany Museum (9). 



The specimen is represented by most of the presacral vertebrae, 

 many ribs, the right arm, the left femur, and a small portion of the 

 skull. Probably only the atlas is missing among the presacral verte- 

 brae, and if this be so then the full number would be twenty-six. 

 The vertebrae being split through are not very well preserved, but 

 their relative sizes and some other points are seen in the figure 

 given. The ribs are slender and, so far as can be seen, all single 

 headed. The arm is not well preserved, and does not show any 

 features not better seen in other Anomodonts. 



The thigh bone is very like that of Oudenodon, having a broad 

 upper end and a narrow middle portion. 



The skull fragment consists of most of the left squamosal and 

 jugal bones, a considerable portion of the maxilla, and most of the 

 back part of the mandible. The bones are very like those of Oudeno- 

 don, but the specimen is removed from that genus by the presence 

 of a small maxillary tooth. The evidence does not show if there 

 have been more, but it is probable. The tooth is moderately flat, 



