NATURAL HISTORY. 
109 
ROOM II.] 
have five toes on each foot., and the head three-shielded. The Hydraspes 
and Phrynops have five toes to the front and four to the hinder feet; 
the former has the head covered with plates, and the latter covered with 
a soft skin, and it has only five vertical plates. The genus Chelys is 
peculiar for having the jaws covered with the fleshy lips; the nose is 
produced, and the lips and throat bearded. The fossil genus, 
Megasternon , has a solid sternum with marginal intergular plates, 
and is peculiar for having some additional plates over the sterno-costal 
suture, like Platysternon among the Emydce. 
The third family or (Trionycid^e, Case 23) are peculiar from having 
the shell covered with a naked skin, and only three toes of each foot 
provided with claws. They, like the two preceding families, are strictly 
carnivorous, and eat their food in the water. Many large specimens of 
this genus are found in the East Indies, and are frequently seen preying 
on human bodies as they float down the Ganges. The genus Emyda 
is peculiar for the legs, when dravra up, being covered by a moveable 
flap placed on the sides of the chest, and the edge of the shell is bony. 
In the other genus, Trionyx , the legs are exposed and the margin of 
the shell is flexible. 
The Marine Tortoises or Turtles (Cheloniam:, Case 23) are distin¬ 
guished by their feet being compressed and fin-shaped; they live princi¬ 
pally on fuci, sea-weeds, shells, and crustaceous animals. The Coriaceous 
Turtle ( Sphargis), which differs from the other Turtles in the bones being 
covered with a continuous coriaceous skin, -while in Chelonia it is 
covered with horny plates, like the other Testudines . Sometimes the 
edges of the plates are produced and imbricate over the others. These 
are the kinds most commonly used as food, and great quantities of one 
species ( Chelonia Midas ) are annually brought to England for that 
purpose. The horny plates of the Imbricated Turtle ( Chelonia 
imbrieata ) afford the best sort of tortoise-shell. 
The Emydosaurians (Case 24) have the appearance of gigantic 
lizards, but they differ from them in the body being covered with 
square bony plates placed in longitudinal lines, in the solidity and 
formation of their skull, and in the vent being longitudinal. They are 
only found in the -warmer climates. 
The Alligators are peculiar to America, and are distinguished from 
the Crocodiles, which are found both in the Old and New World, by 
their feet having the toes free, that is, unconnected by webs, and by 
the canine teeth of the lawer jaw being received in pits in the upper ; 
whereas, in the Crocodiles, they are received in a notch on its margin. 
The Gavials agree with the Crocodiles in regard to their teeth, but 
differ by the muzzle being very long and slender. Specimens of all 
the three genera are in the Collection. The upper jaw of these 
animals is generally, but erroneously, said to be moveable; the mistake 
having arisen from the lower jaw being much produced posteriorly. 
The Amphisbeniaxs (Case 4) have a long cylindrical body 
covered with square imbedded plates, and have some relation to the 
C(Ecik<z. They are equally blunt at both ends, which has led to the 
idea that they walk both backwards and forwards with the same facility, 
—hence their name. They are generally destitute of limbs ; but the 
genus Chirotes is peculiar for having two small rudimentary front legs. 
Most of them have teeth placed on the inner edges of the jaw, but the 
