DIVISIONS OF REPTILIA. 273 
distinguished by its narrow, elongated jaws, forming a kind of 
beak. It attains a length of more than ten feet. 
ORDER V. ICHTHYOPTERYGIA,—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 formation 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 with- 
out any distinct neck. The vertebrae were hollow at both ends 
(amphicelous), and the. spine thus possessed the flexibility and 
power of motion so characteristic of the true fishes. The limbs 
also constituted powerful swimming-paddles (fig. 148), and it is 
probable that there was a vertical tail-fin. 
Much has been gathered from various sources as tOe the 
habits of the /chthyosauri, and their history is one of the most 
— Lea 
INI 
Fig. 148.—Jchthyosaurus communis. 
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 power- 
ful bony arch supporting the fore-limbs proves that they must 
occasionally have 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, especially in the dusk, seems 
to be rendered certain from the size of the pupil and the enor- 
mous 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, 
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