1082 



CLASS REPTILIA. 



shorter than in that genus, and have scarcely any intervening 

 space, but in one of the species from the Oxford Clay they 

 have the same form as in the latter. The general arrangement of 

 the ventral bones of the pelvis is shown in the woodcut. In the 

 huge P. macromerus, of the Kimeridge Clay, the length of the 

 lower jaw was nearly six feet, and that of the femur one yard, by 

 which some estimate can be formed of the gigantic dimensions 

 attained by the entire animal. Pliosaurs were widely distributed 

 over Europe, and have been described from England, Germany 

 (as Ischyrodofi), France (as Lioftlem'odon), and Russia (as Spondylo- 

 saurus). No remains of this genus have, however, been hitherto 



— *> 



Fig. 1005. — Anterior (1) and lateral (2) aspects of an anterior cervical vertebra of Pliosatirus 

 macromerus ; from the Kimeridge Clay. One-fifth natural size. (After Phillips.) 



recorded from America. The less specialised characters of the 

 Oxfordian forms, as shown by the structure of the teeth, and the 

 longer radius and ulna, indicate affinity with Peloneustes. 



Finally, it may be mentioned that in addition to the names 

 already recorded the terms Pifitomerus, Orophosaurus, and Uro- 

 naules have been applied by Professor Cope to Sauropterygian re- 

 mains from the Cretaceous of North America ; while a tooth from 

 the Kimeridgian of France, described under the name of Hcemato- 

 saurus, has likewise been shown to belong to this order, although 

 originally regarded as Crocodilian. 



Order III. Chelonia. — With the Tortoises, Turtles, and their 

 allies, we enter upon the consideration of the first of the existing 

 orders of Reptiles. In this order the cervical and dorsal vertebrae 

 are not numerous ; the body is short and wide, and has a more or 

 less complete bony shell, of which the ventral part, or plastron, con- 

 sists of few elements of dermal origin, while the dorsal, or carapace, 

 may be in great part of endoskeletal origin. There is generally a 

 horny epidermal exoskeleton. The skull may occasionally have two 

 temporal arcades, but more generally only the lower one is present 

 (fig. 1007), and in some cases even that may be absent. The nares 

 (fig. 1024) are single and terminal; the premaxillse very small; and 

 there is no parietal foramen in the adult ; but there is a distinct 



