EXTINCT ORDERS OF REPTILES. 475 



Nothosaunis are from the Trias, and are chiefly characteristic 

 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 

 (fig. 207), both jaws seem to have been altogether destitute of 

 teeth ; but in Dicynodon (fig. 207) there were two long tusks, 

 growing from persistent 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. This last genus, however, 

 is placed by Huxley amongst the Lacertilia. 



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 ver- 

 tebrae 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 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 seem 

 to have been sheathed in horn, so as to constitute a kind of 

 beak. A ring of bony plates occurs in the sclerotic coat of 

 the eye. The pectoral arch consists of a scapula and distinct 

 coracoid bone, articulating with the sternum as in Birds, but 

 no clavicles have hitherto been discovered. The fore-limb 

 (fig. 208) consists of a humerus, ulna and radius, carpus, and 

 hand of four fingers, of which the inner three are short and un- 

 guiculate, whilst the outermost is clawless and is enormously 

 elongated. Between this immensely-lengthened finger, the 

 .side of the body, and the comparatively small hind-limb, there 

 must have been supported an expanded flying-membrane or 



