EXTINCT ORDERS OF REPTILES. 419 



of its middle division, the Muschelkalk. Placodus is another 

 genus, also from the Muschelkalk, and is characterised by the 

 extraordinary form of the teeth, which resembled those of many 

 fishes in forming broad crushing plates, constituting a kind of 

 pavement. 



ORDER VII. ANOMODONTIA, Owen (= Dicynodontia, Hux- 

 ley). The leading characters of this order are to be found in 

 the structure of the jaws, which appear to have been sheathed 

 in horn, so as to constitute a kind of beak, very like that of the 

 Chelonians. In the genera Rhynchosaurus and Oudenodon 

 both jaws seem to have been altogether destitute of teeth, but 

 in Dicynodon there were two long tusks, growing from persist- 

 ent pulps, placed one on each side in the upper jaw. The 

 pectoral and pelvic arches were very strong, and the limbs were 

 well developed and fitted for walking, and not for swimming. 



Dicynodon and Oudenodon are known only from strata of 

 supposed Triassic age in South Africa and India, but Rhyncho- 

 saurus occurs in the Trias of Europe. 



ORDER VIII. PTEROSAURIA. This order includes a group 

 of extraordinary flying Reptiles, all belonging to the Mesozoic 

 epoch, and exhibiting in many respects a very extraordinary 

 combination of characters. The most familiar members of the 

 order are the so-called " Pterodactyles," and the following are 

 the characters of the order : 



No exoskeleton is known to have existed. The dorsal 

 vertebrae are proccelous, and the anterior trunk - ribs are 

 double-headed. There is a broad sternum with a median 

 ridge or keel, and ossified sternal ribs. The jaws were always 



Fig. -if>$.Pterodactyhis brevirostris. Skeleton and restoration. 



armed with teeth, and these were implanted in distinct sockets. 

 In some forms (Ramphorhynchus) there appear to have been 

 no teeth in the anterior portion of the jaws, and these parts 



