30 NATURAL HISTORY. [UPPER FLOOR. 
The third group ( Trionycidce) 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 drawn 
up, being covered by a moveable flap placed on the sides of 
the chest. 
The Marine Tortoises or Turtles ( Cheloniadae ) are dis¬ 
tinguished by their feet being compressed and An-shaped; 
they live principally on fuci, sea-weeds, shells and crus- 
taceous animals. These are the kind most commonly used 
as food, and great quantities of one species ( Chelonia 
Midas) are annually brought to England for that pur¬ 
pose. The horny plates of the Imbricated Turtle ( Chelo - 
nia imbricatd) afford the best sort of tortoise-shell. Over 
the mantel-piece is a large specimen, caught on the coast 
of Dorsetshire, of the Coriaceous Turtle (Sphargis), which 
differs from the other Turtles in the bones being covered 
with a continuous coriaceous skin instead of horny plates. 
The Emydosaurians (Cases 1 and 2) have the appear¬ 
ance of gigantic lizards, but they differ from them in the 
body being covered with square bony plates placed in longi¬ 
tudinal 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 dis¬ 
tinguished 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 
lower 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 Amfhisbenians (Case 2,) have a long cylindrical 
body covered with square imbedded plates, and have some 
relation to the Ccecilice. They are equally blunt at both 
