324 
COMPARATIVE ZOOLOGY. 
skin, and eyes with movable lids; a muscular gizzard; a 
long, compressed tail; and four legs, with feet more or 
less webbed, and having five toes in front and four be¬ 
hind. The existing species are confined to tropical rivers, 
and are carnivorous. The eggs are covered with a hard 
shell. 
There are three representative forms: the Gavial of the 
Ganges, remarkable for its long snout and uniform teeth; 
the Crocodiles, mainly of the Old World, whose teeth are 
unequal, and the lower canines fit into a notch in the edge 
of the upper jaw, so that it is visible when the mouth is 
Fig. 303.—Alligator (A. Mississippiemis). Southern States. 
closed; and the Alligators of the New World, whose ca¬ 
nines, in shutting the mouth, are concealed in a pit in the 
upper jaw. The toes of the Gavials and Crocodiles are 
webbed to the tip; those of the Alligators are not more 
than half-webbed. 
In the mediaeval ages of geological history, the class of 
Reptiles was far more abundantly represented than now. 
Among the many forms which geologists have unearthed 
are numerous gigantic Saurians, which cannot be classi¬ 
fied with any of the four living orders. Such are the 
Ichthyosaurus , Plesiosaurus , Pterodactyle , Megalosaurus , 
and Iguanodon. 
