ANOMODONT REPTILES. 



359 



A small mandible sliovvs the crowns of two teeth in fairly good 

 preservation. They are seen to agree pretty closely with those of 

 Pristerodon. Thongh the teeth are rather more robust, they are 

 i-eally relatively very much smaller. One might incline on the 

 evidence of the teeth to place these large sj^ecimens in the 

 genus Pristerodon, but the structure of the parietal region differs 

 so considerably that it is necessary to place them in a different 

 genus. The snout agrees so closely with Dicynodon except for 

 the presence of the molars, that one has to consider whether it 

 might not be possible that all species of Dicynodon had molars 

 when young which they lost later. This, however, is hardly 

 possible. In no species of Dicynodon have molars ever been 

 detected — even where the skulls are manifestly of young animals. 

 Of Dicynodon platyceps we know over a dozen skulls, from small 

 ones about 3 inches to others over a foot in length. But in none 

 is there any trace of molars. Further, the peculiar condition of 

 the intertemporal region found in the present species is unknown 



Text-fia:m-e 3. 



Bones of the frontal and parietal regions of the skull of Tropidostoma 



microtrema (Seelej-). About \ nat. size. 



For lettering see text-fig. 1, ji. 356. 



in any species of Dicynodon. We may, therefore, safely conclude 

 that Dicynodon raicrotrema Seeley must be jalaced in a distinct 

 genus. Another specimen, figured by Seeley in 1889, was an 

 occiput which he named Dicynodon {Tropidostoma) dunni. 

 Lydekker i-egarded this specimen — quite rightly, I think — as 

 belonging to the same sj^ecies as that named D. microtrema. And 

 if this be so we must accept the generic name Tropidostoma 

 for the type. 



Though there is no complete skull in the collection, one is 

 fairly complete, and there are so many snouts, occiputs, and 

 other portions, that practically every detail of the structure can 

 be made out. 



The skull, in what appears to be an adult male, measures from 

 the snout to the plane cutting the posterior borders of the 

 squamosals 266 mm., and the greatest width across the squamosals 

 is about 220 mm. 



