220 HISTORICAL PALEONTOLOGY. 



Plctcodus, again, the teeth are in distinct sockets, but resemble 

 those of many fishes in being rounded and obtuse (fig. 153), 

 forming broad crushing plates 

 adapted for the comminu- 

 tion of shell-fish. There is a 

 row of these teeth all round 

 the upper jaw proper, and a 

 double series on the palate, 

 but the lower jaw has only a 

 single row of teeth. Placodus 

 is found in the Muschelkalk, 

 and the characters of its den- 

 tal apparatus indicate that 

 it was much more peaceful 



in it3 habitS tllan ltS aSSO 

 chelkalk, Germany. CJatCS the NotllOSaur and Si- 



mosaur. 



The Triassic rocks of South Africa and India have yielded 

 the remains of some extraordinary Reptiles, which have been 

 placed by Professor Owen in a separate order under the name 

 of Anomodontia. The two principal genera of this group are 

 Dicynodon and Oudenodon, both of which appear to have been 

 large Reptiles, with well-developed limbs, organised for pro- 

 gression upon the dry land. In Oudenodon (fig. 154, B) the 

 jaws seem to have been wholly destitute of teeth, and must 

 have been encased in a horny sheath, similar to that with 

 which we are familiar in the beak of a Turtle. In Dicynodon 

 (fig. 154, A), on the other hand, the front of the upper jaw 

 and the whole of the lower jaw were destitute of teeth, and 

 the front of the mouth must have constituted a kind of beak; 

 but the upper jaw possessed on each side a single huge conical 

 tusk, which is directed downwards, and must have continued 

 to grow during the life of the animal. 



It may be mentioned that the above-mentioned Triassic 

 sandstones of South Africa have recently yielded to the re- 

 searches of Professor Owen a new and unexpected type of 

 Reptile, which exhibits some of the structural peculiarities 

 which we have been accustomed to regard as characteristic 

 of the Carnivorous quadrupeds. The Reptile in question has 

 been named Cynodraco, and it is looked upon by its distin- 

 guished discoverer as the type of a new order, to which he has 

 given the name of Theriodontia. The teeth of this singular 

 form agree with those of the Carnivorous quadrupeds in con- 

 sisting of three distinct groups namely, front teeth or incisors, 

 eye teeth or canines, and back teeth or molars. The canines 



