250 VERTEBRATE ANIMALS. 



Oedbe VI. Saueopteetgia (Gr. saura, lizard; pterux, 

 wing). — The Reptiles belonging to this order agree with the 

 last in being all extinct, and in being confined to the Se(?ond- 

 ary period of geology. The best known are the Plesiosauri, 

 which resembled the Ichthyosauri in having all the limbs con- 

 verted into swimming-paddles, but differed in several respects, 

 of which the most obvious is the great elongation of the neck 

 (Fig. 136). The Plesiosauri were gigantic marine Reptiles, 



Fig. 126. — PUsiosaurus dolichodeirus. 



chiefly characteristic of the formations known as the Lias and 

 Oolites. As regards the habits of the Plesiosaurus, Dr. Cony- 

 beare concludes : " That it was aquatic is evident from the form 

 of its paddles ; that it was marine is almost equally so from the 

 remains with which it is universally associated ; that it may 

 have occasionally visited the shore, the resemblance of its ex- 

 tremities to those of the Turtle may lead us to conjecture ; its 

 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 organization 

 which so admirably fits the Ichthyosaurus to cut through the 

 waves." As its breathing-organs are such that it must of ne- 

 cessity have required to obtain air frequently, it may be in- 

 ferred " 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 pei^ 

 haps have lurked in shoal-water along the coast, concealed 

 among the sea-weed, and, raising its nostrils to a level with 

 the surface from a considerable depth, may have found a se- 

 cure 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." 



Oedee VII. Pteeosatjeia (Gr. pteron, wing; sawra, 

 lizard). — The Reptiles of this order are all extinct, and, like 

 those of the preceding orders, are exclusively confined to the 



