448 MANUAL OF ZOOLOOY. 



movements, however, must have been very awkward on land ; 

 and its long neck must have impeded its progress through the 

 water, presenting a striking contrast to the organisation which 

 so admirably fits the Ichthyosaurus to cut through the waves." 



Fig. 176. — Plesiosaurtts dolichodeii-us. 



As its respiratory organs were such that it must of necessity 

 have required to obtain air frequently, we may conclude " that 

 it swam upon or near the surface, arching back its long neck 

 like a swan, and occasionally darting it down at the fish which 

 happened to float within its reach. It may, perhaps, have 

 lurked in shoal water along the coast, concealed amongst the 

 sea-weed ; and raising its nostrils to a leVel with the surface 

 from a considerable depth, may have found a secure retreat 

 from the assaults of powerful enemies ; while the length and 

 flexibility of its neck may have compensated for the want of 

 strength in its jaws, and its incapacity for swift motion through 

 the water." 



The geological range of the Plesiosaunis is from the Lias to 

 the Chalk inclusive, and specimens have been found indicating 

 a length of from eighteen to twenty feet. 



Of the other genera of the Sauropierygia, Simosaurus and 

 Nothosaurus are from the Trias, and are chiefly characteristic 

 of its middle division, the Muschelkalk. Placodus is another 

 genus, also from tlie 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 RhynchosaArus and Oudenodon, 

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

 in Dicynodon there were two long tusks, growing from persistent 

 pulps, pkced 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 



