74 Transactions of the South African Philosophical Society. 



palaeontologists, including Lydekker * and Seeley,f the latter of 

 whom expressed the opinion in 1887 that Trityloclon was a " Buno- 

 theroid Eodent." 



In 1894 Seeley, ;[ as the result mainly of his discovery of Therio- 

 donts with flattened molar teeth, gave up his earlier view and 

 came to the conclusion that " Tritylodon w&s a Eeptile," but admitted 

 the possibility of its belonging to " a group of animals intermediate 

 between Mammals and Theriodonts." In 1895 he definitely placed 

 Trityloclon in the, " Gomphodontia." As, in 1898, Seeley § expressed 

 the opinion that the Theriodonts are not the ancestors of the 

 Mammals, we may assume that he has abandoned the view of 1894 

 that Trityloclon may possibly belong to a group intermediate between 

 Mammals and Theriodonts. 



Let us look at the evidences which Seeley brings forward in 

 support of the view that Trityloclon is a Theriodont and not a 

 Mammal. 



In the first place the orbit is said to have been closed behind as in 

 Theriodonts. On this point the specimen gives very little evidence. 

 Owen considered that the orbit was probably incomplete behind, 

 and until a more perfect specimen is discovered it will be impossible 

 to definitely settle the point. As, however, many Mammals have the 

 orbit closed behind by bone the point is not of very much importance. 

 A much more important point is whether Trityloclon had a distinct 

 postfrontal or postorbital bone. By Owen the pair of bones behind 

 the frontals are believed to be the parietals ; by Seeley they are 

 looked upon as the inner parts of the postfrontals. If they are 

 postfrontals or rather postorbitals they are unlike the postorbitals of 

 the known Theriodonts. In Gomphognathus and Trirachodon the 

 Theriodonts with which Seeley compares Tritylodon, the frontals pass 

 well back between the inner parts of the postorbitals, but in Tritylo- 

 clon the frontals are prevented from passing backwards by the 

 median union of the two bones behind. The bones thus resemble 

 rather mammalian parietals than Theriodont postorbitals. Even, 

 however, should the bones be ultimately proved to be postorbitals, 

 it must be remembered that postorbitals occur in Omithorhynchus. 



In the second place Seeley points out that in Theriodonts the 

 snout has a bulbous appearance, owing to the widening of the 

 maxillary bones by the roots of the large canines, while in Tritylodon 



* K. Lydekker, Cat. Fossil Mammals, Brit. Mus. 



f H. G. Seeley, " On Parts of the Skeleton of a Mammal, &c." Phil. Trans., 

 1888, p. 141. 



I Ibid., " The Origin of Mammals." Int. Cong. Zool., Cambridge, 1898. 



§ Ibid., " The Keputed Mammals from the Karroo Formation of Cape Colony.' 

 Phil. Trans., 1895, p. 1025. 



