1888.] of Reptilian Character in Mammalian Teeth. 135 



might be regarded as mammalian. This character has been figured 

 from the lower jaw, and in 1878 it was remarked* "among Croco- 

 diles, I recognise in the well-known wavy outline of the jaws a 

 demarcation of teeth into regions which have a fair right to be 

 named incisors, canines, premolars, and molars, and constitute a 

 dentition as Theriodont in principle, but not so specialised, as is seen 

 in the South African fossil group. In the Crocodile the regions 

 are easily recognised by the form, size, and characters of the tooth 

 sockets when all the teeth are drawn, especially in the lower jaw. 

 The incisors occupy a fiat or slightly concave region below the 

 premaxillary bone. Then at the head of the crest is the large 

 canine placed between the premaxillary and maxillary bones. Next 

 succeeds a portion of jaw with concave outline occupied by small 

 teeth, which sometimes become larger from before backward ; these 

 are the premolars. And, lastly, there are teeth in another con- 

 cave region which have the position of molars ; these may, in the 

 young animal, all be contained in a groove, with sockets scarcely 

 better indicated than among Ichthyosaurs or some Cetaceans. In 

 many Teleosaurs and Plesiosaurs the incisor teeth are relatively 

 large, and the succeeding molars are smaller ; and in the Ornitho- 

 saur Dimorphodon the incisor teeth are exceptionally large, as com- 

 pared with the molars. The teeth of South African reptiles termed 

 Theriodontia differ from such types chiefly in the development of large 

 canines. The incisors remain large, the canines are larger, and the 

 molars relatively small, as may be seen in such genera as Cynodraco 

 and Lycosaurus. In this group the incisors have both crown and root 

 compressed from side to side. The crown often has a prominent 

 sharp chisel-like external cusp, and a small internal cusp which gives 

 the tooth a mammalian aspect. This character is well seen in the 

 Russian genus D enter osaurus as figured by Eichwald and by 

 Mr. Twelvetrees, the latter specimen being in the National Collection. 

 A similar condition, but with the inner cusp less conspicuous, is seen 

 in a new genus from South Africa allied to Veuierosanrus, here 

 figured, which may be named Glaridodon. In this tooth, besides the 

 elevated outer and inner cusps, there are on both sides elevated lateral 

 borders to the crown, so that it includes a concave area, which in 

 mode of formation of the concavity may be compared to the concave 

 crown of the molar tooth of Ornithorhynchus, though the proportions 

 of the tooth are dissimilar. Yet if a tooth of this type is supposed to 

 lose its root by degeneration, it might show a close approximation to 

 the tooth of such a mammal as Ornithorhynchus. The canine teeth 

 in Theriodonts, like those of some of the lower mammalian orders, 

 appear to be placed in the maxillary bone, and not in the suture 

 between that bone and the premaxillary, as in the higher mammals. 

 * " On Procolophon," ' Geol. Soc. Quart. Journ.,' vol. 34, 1878, pp. 80-1-5. 



