DIVISIONS OF REPTILIA. 249 



distinguished by its narrow, elongated jaws, forming a kind 

 of beak. It attains a length of more than ten feet. 



OKDER V. ICHTHYOPTEEYGIA (Gr. ichthus, fish ; pterux, 

 wing). In this order are included a number of gigantic, fish- 

 like Reptiles, which are all extinct, and are characteristic of 

 the Secondary period of geology, and especially of the forma- 

 tion known as the Lias. The chief characters by which they 

 are distinguished have reference to their purely aquatic life, 

 for there can be no doubt that they were inhabitants of the 

 sea. Thus the body was fish-like, without any distinct neck. 

 The vertebras were hollow at both ends (amphiccelous) , and 

 the spine thus possessed the flexibility and power of motion 

 so characteristic of the true fishes. The limbs also consti- 

 tuted powerful swimming-paddles (Fig. 125), and it is proba- 

 ble that there was a vertical tail-fin. 



Much has been gathered from various sources as to the 

 habits of the Ichthyosauri, and their history is one of the most 

 interesting chapters in the geological record. That they 

 chiefly kept to open seas may be inferred from their strong 

 and well-developed swimming apparatus ; but the presence of 

 a powerful bony arch supporting the fore-limbs proves that 



FIG. 125. Ichthyosaurus communte. 



they must have occasionally betaken themselves to the land. 

 That they were tenants of stormy waters, or were in the habit 

 of diving in search of 'prey, has been inferred from the fact 

 that the eyeball is protected from pressure by a ring of bony 

 plates. That they possessed great powers of vision, espe- 

 cially in the dusk, seems to be rendered certain from the size 

 of the pupil and the enormous width of the bony cavities 

 (orbits) which contained the eyes. Lastly, that they were 

 carnivorous and predacious in the highest degree is shown by 

 their wide mouths, long jaws, and numerous powerful and 

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

 petrified droppings, which are known as " coprolites," and 

 which contain in abundance undigested fragments of fishes 

 and other marine animals. 



