154 



REPTILIA. 



In the hinder dorsal and lumbar region the ribs are curiously expanded 

 and imbricating. Three or four vertebrae are comprised in the sacrum, 

 and the tail must have been small, apparently without free caudal ribs. 

 The scapula exhibits its great spine. The ilium is a little expanded, 

 projecting further backwards than forwards, and all three elements of the 

 pelvis enter the acetabulum. The vacuity between the pubis and ischium 

 is distinct. The typical species Cynognathus crateronotus, and allied 

 species, occur in the Karoo Formation of Cape Colony. 



FIG. 97. 



Tritylodon longcevus ; skull wanting hinder occipital end, from the palatal (A) 

 and upper (B) aspects, two-thirds nat. size. Karoo Formation (Permian 

 or Triassic) ; Basutoland, South Africa. (After Owen.) 



Tritylodon (fig. 97). Some Theriodonts exhibit the molariform teeth 

 not laterally compressed but transversely expanded and adapted for 

 grinding. An extreme example probably of this type is the imperfect 

 skull from the Karoo Formation of Basutoland, described under the name 

 of Tritylodon longcevus and commonly ascribed to a mammal. The pair 

 of incisor or canine-like teeth in front seem to have grown from a 

 persistent pulp. The molariform teeth preserved bear three longitudinal 

 series of tubercles, and their roots are either divided or impressed with a 

 very deep vertical groove 011 the outer face. 



An extraordinarily mammalian fore limb and manus from 

 the Karoo Formation of Cape Colony, described under the 

 name of Theriodesmus phylarchus, probably belongs to a Therio- 

 dont, and two interpretations of the characters of the manus 



