A history of British reptiles / By Thomas Bell...Illustrated by more than forty woodcuts.

  • Bell, Thomas, 1792-1880.
Date:
1839
Catalogue details

Licence: Public Domain Mark

Credit: A history of British reptiles / By Thomas Bell...Illustrated by more than forty woodcuts. Source: Wellcome Collection.

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    or upper part of the case, is moveable, so that the animal has the power, when the limbs and tail are withdrawn within it, to close that moveable piece against the posterior part of the sternum ; and in the genus Pyx7s the anterior portion of the sternum exhibits this peculiarity in a still more remarkable degree. But it is in the genera T'errapene, Kinosternon, and Sternothenus, all of them aquatic or palustrine forms, that this peculiarity is the most obvious. In the first-named genus especially, the sternum is formed of two distinct valves, moveable upon a single cartilaginous hinge, and capable of com- pletely closing the bony box, of which it thus forms a double lid ; within this admirable shelter the animal is wholly in- cluded, and, if disturbed, resists, by means of its powerful muscles, every attempt to open it. The general form of the carapax, or upper part of the shell, is also admirably adapted to the habits of the different groups of which this order is composed. In the land Tortoises it is strong, compact, ele- vated, and regularly arched, for the purpose of resisting the numerous injuries to which their localities, and especially their extreme slowness of movement, must otherwise expose them. In the aquatic species, on the contrary, it is remarka- bly flattened, especially in the genus T'rionyx, which has also the margins of the ribs free towards their extremities, and the whole body covered with a coriaceous skin, which is free at the edges, and serves the same purpose as the flattened lateral fins of the flat fishes, such as the sole and plaice,— namely, to enable them to scuttle themselves under the mud or sand at the bottom of the rivers or lakes in which they reside. These last have also a very long and retractile neck, by which they are able, when thus concealed, to seize fish which pass immediately above them, by suddenly stretching out the neck, and then as suddenly withdrawing it. The land Tortoises, which are exclusively vegetable feeders, are slow in their motions, the limbs being clumsy and club-