Page:Natural History, Reptiles.djvu/61

Rh The subjects which compose this Order are few in number, and are all comprised in a single Family, which we shall presently describe more in detail. They are natives of both hemispheres, but are confined to the warmer regions of both, neither Europe nor Australia possessing any known species: they all inhabit fresh waters.

Messrs, Duméril and Bibron enumerate the following characters as proper to this family. The body is depressed, lengthened, protected on the back with solid and keeled scutcheons, or shields;

the tail is longer than the trunk, compressed, the plates here set in rings, and rising into a ridge of pointed crests; the limbs are four in number, short; the toes of the hind feet united by a swimming membrane; three claws only on each foot; the head is flattened, lengthened into a muzzle, in the front of which are the nostrils, not far apart, upon a fleshy tubercle, furnished with moveable suckers; the gape opens beyond the base of the skull; the tongue is fleshy, entire, adherent, not protractile; the teeth are conical, simple, hollowed towards the root, unequal in length, but placed in a single row. The cavity at the root of each tooth serves as a case or sheath for the germ of the tooth destined to replace it, which is to be of greater bulk;