74 Rivbe Tortoises, REPTILES. Marine Tortoises. 
in front and pointed, the bones composing it being 
nearly naked. The jaws are horny, and covered witli 
a dependent, fleshy fold of skin resembling lips, and 
which can cover the mouth. The nostrils are pro- 
longed into a thin cylindrical tube, like a small mov- 
able probcscis. Their carapace is very broad, and 
nearly flat— fig. 23. It is soft, destitute of plates, and 
covered with a flexible and cartilaginous sort of skin, 
which extends al^ round the edges of the shell. These 
Fig. 23. 
Carajiace of Trionyx. 
edges are soft, and destitute of bones, and the ribs are 
only united together and to the vertebraj above, wliilst 
they are separate below. The plastron or breastplate 
is formed of a ring of bones, the centre not being ossi- 
fied, and covered with a continuous skin. In adult 
individuals these bones are furnished with rough 
callosities on the prominent parts. The legs are short 
and strong, and nearly of equal length behind and 
before. 
None of the species are European, all that have as 
yet been described being found in the large rivers and 
deep lakes of the hotter portions of the globe. The 
Nile and the Niger in Africa ; the Euphrates and 
Ganges in Asia ; the Mississippi and Ohio in America, 
are the principal places of abode of these animals. 
Some of them attain a very large size. Pennant men- 
tions individuals which weighed seventy pounds, and 
he had one which lived in his possession for three 
months that weighed twenty pounds, and was twenty 
inches long in the shell. The neck measured thirteen 
and a half inches in length. Individuals of the species 
known as the Sewteree {Chitra Indica), a native of 
the- Ganges and other rivers of India, have been taken, 
which, according to Dr. Cantor, weighed two hundred 
and forty pounds. 
The River tortoises are in a great measure noctur- 
nal animals. At night, when thej' consider themselves 
free from danger, they come forth from the water to 
stretch themselves out on the rocks in the little islets, 
or take up a position on the trunks of trees overturned 
in the rivers, but from which they precipitate them- 
selves again into the water at the least noise or appear- 
ance of danger. They are very voracious, and very 
nimble in pursuit of their prey. This consists of fishes, 
reptiles, and mollusca, to which they are continually 
giving chase, and which they pursue while swimming. 
They in their turn are eagerly sought after by man, for 
their flesh is much esteemed as an article of food. In 
order to catch them it is necessary to angle for them, 
and to bait the hook with live fishes or other small 
animals, to which motion must be given, for they will 
not touch carrion or motionless prey. When they 
seize their prejq or when they are called to defend 
themselves, they dart their head and long neck forward 
with the rapidity of an arrow. They bite severely, 
nor will they let go their hold without taking out the 
piece seized. Their bite in consequence is much 
dreaded by the fishermen, who generally cut olf their 
heads as soon as they are caught. The males appear 
to be less numerous than the females, or at least they 
are less frequently seen near the shore, the females 
being obliged to come to land to lay their eggs. These 
they de])osit in large holes which they dig out in the 
sand, of sufficient size to hold fifty or sixty. They are 
white, spherical, with a shell which is solid, but only 
membranous or very slightly calcareous. 
THE TYRSE OR SOFT TORTOISE OF THE NILE 
{Trmiyx Niloticus ) — represented in Plate G, fig. 7 — 
is a good illustration of the family. The carapace is 
rather convex in the centre, oval or somewhat orbicular 
in shape, covered with a skin which is coriaceous, 
rough to the touch, and of a greenish colour or blackish- 
brown, dotted with white or yellowish spots. The 
breastplate is white, the rough callosities bluish. The 
head is rather long, the jaws very strong, the lips 
much developed and thick, and the tall is conical, 
thick, and pointed. The Tyrse (for by that name it 
is known on the banks of the Nile) sometimes reaches 
three feet in length. It inhabits the river Nile, but is 
found in other rivers both of West and North Africa. 
These animals are said to he very destructive to the 
young crocodiles, devouring them in great numbers as 
soon as hatched. 
This is the only species of Trionyx that inhabits the 
Nile. Several other species are found in the rivers in 
India and America, but we have not space to mention 
them. 
MARINE TORTOISES or TURTLES 
(Cheloniidce). 
Of all the species of the Tortoise race, the Marine 
species or Turtles are those which have more especially 
attracted the attention of mankind from the earliest 
periods of antiquity. Aristotle distinguishes them 
from all the others by the term Tkalassios (DaXaasiog 
or SaXuTTiog), a term derived from the Greek, meaning 
those animals which “ frequent the sea.” There are 
two groups into which they may be divided, according 
to the structure of the carapace, viz., those which have 
this part of their shell, as well as their neck and feet, 
covered with more or less hard and horny scales, and 
those the carapace of which, and the external parts of 
their body, are covered with a hard, thick, horny skin. 
The structure of the limbs is one of the most remark- 
able characters of this family, and distinguishes them 
