B. M. S. Watson — Neiv Cynodont from Cape Colony. 147 



They have, however, transversely widened molar teeth. Triholodon 

 differs in its raucli more slender jaw and scattered teeth. It is thus 

 certain that our jaw, for which I propose the name Fachygenelus monus, 

 belongs not only to a new genus and species, but also probably to 

 a new family of ' Cynodonts '. 



It may be of interest to discuss briefly the derivation of the molar 

 teeth oiDiademodon, not only for the intrinsic interest of the subject, 

 but also for its bearing on the Tritubercular and allied theories of 

 mammalian tooth development. As Broom has pointed out, the 

 resemblance between Cynognathm and Diademodon is so close as to 

 show that the two tvpes with Trirachodon form a compact group of 

 ' Cynodonts', and that it is very probable that the Trirachodon molar 

 has been derived from a condition similar to that of Diademodon., 

 which in turn comes from a type like that of Cytiognathus. There is 

 also no doubt that all three are descended from ' Therocephalian ' 



Fig. 3. 



A. The three last molars of Diademodon hrowni. x 3. 

 A'. The last molar of D. hrowni, external aspect. X 8. 



B. The three last molars of D. entomoplionus. x 3. 



C. ,, ,, jD. mastacus. x 3. 



ancestors, having simple conical molars, of which those of the maxillae 

 bite outside the series in the lower jaw. In Theriodonts modification 

 of such teeth apparently invariably begins by the addition of little 

 cusps in front and behind the main primitive cusp : cf. Cynognathus, 

 Nythosaurus, Qalesaurus, Triholodon. If we examine the last upper 

 molar of Diademodon hrowni, Seeley, we find a tooth consisting of 

 a high backwardly curved cusp, whose anterior border is obscurely 

 crenated ; immediately behind this large cusp are two much smaller 

 ones. On the inner side of the main cusp is a short, heavy cingulum, 

 divided into two small cusps. This tooth practically only differs 

 from that of Cynognathus in the presence of the cingulum. The next 

 tooth in front has a similar main cusp, with two smaller posterior 

 cusps. The cingulum is, hovfever, much further developed, and the 

 anterior of the two cusps which it bears is worn down, lying at the 



