VERTEBRATA: REPTILIA. 



561 



stormy seas, or were in the habit of diving to considerable 

 depths, is shown by the presence of a ring of bony plates in 

 the sclerotic, protecting the eye from injury or pressure (fig. 

 313). That they possessed extraordinary powers of vision, 



Fig. 313. Skull of Ichthyosaurus, showing the. sclerotic plates. 



especially in the dusk, is certain from the size of the pupil, and 

 from the enormous width of the orbits. That they were car- 

 nivorous and predatory in the highest degree is shown by the 

 Wide mouth, the long jaws, and the numerous, powerful, and 

 pointed teeth. This is proved, also, by an examination of 

 their petrified droppings, which are known to geologists as 

 " coprolites," and which contain numerous fragments of the 

 scales and bones of the Ganoid fishes which inhabited the 

 same seas. 



ORDER VI. SAUROPTERYGIA, Owen ( = Plesiosauria, Hux- 

 ley). This order of extinct reptiles, of which the well-known 

 Plesiosaurus may be taken as the type, is characterised by the 

 following peculiarities : 



The body, as far as is known, was naked, and not furnished 

 with any horny or bony exoskeleton. The bodies of the vertebra 



Fig. 314. Plesiosaurus dolichodeirus. 



were either flat or only slightly cupped at each end, and the neural 

 arches were anchylosed with the centra^ and did not remain dis- 

 tinct during life. The transverse processes of the vertebra were 

 long, and the anterior trunk-ribs had simple, not bifurcate heads. 

 No sternum or sternal ribs are known to have existed, but there 

 were false abdominal ribs. The neck (fig. 314) in most was greatly 

 elongated, and composed of numerous vertebra. The sacrum was 

 composed of two vertebra. The orbits were of large size, and there 



2 N 



