222 EXTINCT ORDERS OF REPTILES. 



we meet with types such as Plioscmrus and the related genera 

 JDiscosaurus (or Elasmosaurus), and Cimoliosaurus. 



Order VII. Anomodontia. — The members of this order 

 are especially characterised by the stmcture of the mouth, the 

 jaws being converted into a kind of teak, whieh was prohably 

 sheathed in horn, and resembled the jaivs of a Turtle. Some- 

 times the mouth appears to have been wholly destitute of teeth, 

 but in other cases there was a single "pair of teeth implanted in 

 the upper jaiv, groioing from persistent pidps, and assuming the 

 cluiraeter of great tusks. The dorsal vertebroi are biconcave, 

 and the anterior trunk-ribs have bifurcate heads. The sacrum 

 is large, composed of several vertebrce. Tlie animal seems to 

 have been organised for terrestrial progression, the pectoral and 

 pelvic arches being strong, and the limbs well developed. 



According to Prof. Huxley, the form of the body in the 

 Anomodonts was probably like that of the Lizards ; but the 

 vertebrae are of a Crocodilian type, and though the skull 

 exhibits Lacertilian characters, the jaws remind us more of 

 the Chelonians. 



By Owen the genera Dicynodon, Oudenodon, and Rhyncho- 

 saurus are included in this order ; but the last of these is 

 regarded by Huxley as a Lacertilian. In Dicynodon (fig. 

 571, a), the anterior portions of the jaws appear to have 

 been altogether toothless ; and they form a kind of beak, 

 which was probably sheathed in horn. The lower jaw has 

 no teeth ; but each superior maxilla carries an enormous 

 tusk-like tooth growing from a persistent pulp. These great 

 canines pass downwards outside the forepart of the lower 

 jaw, about one-third of their length being concealed within 

 their sockets. In minute structure they consist of simple, 

 compact, non-vascular dentine, with a thin layer of enamel ; 

 and their points are simply conical and not bevelled or chisel- 

 shaped. Probably they were used solely as weapons of offence 

 and defence. In Oudenodon, on the other hand, the mouth 

 is beak-shaped (fig. 571, b), and seems to have possessed no 

 teeth of any kind. Dicynodon and Oudenodon are known 

 only from strata of supposed Triassic age in India and South 

 Africa. 



Order VIII. Pterosauria (Omithosauria, Seeley). — This 



