The Mud Tortoises, _Cistudo_, sometimes called the Yellow Tortoise (Fig. 36) are very abundant in Europe. They are found in Greece, Italy, Spain, Portugal, and in the southern provinces of France; also in Hungary, Germany, and as far north as Prussia. They inhabit lakes, marshes, and ponds, at the bottom of which they bury themselves in the mud. Occasionally they come to the surface of the water, and remain there for hours. They live principally upon insects, mollusks, aquatic worms, and small fishes. Although the flesh of the Mud Tortoise is far from being palatable, it is nevertheless eaten in countries where they are common. [Illustration: Fig. 37.--Emydes Caspica.] [Illustration: Fig. 38.--Chelys matamata.] The _Emydes_ are divided into four considerable groups, namely, the European group, of which Fig. 37, _E. Caspica_, is typical; the American group, containing twelve or fourteen species; the African _Emys_; and the Oriental group of twelve species. The _Pleuroderes_ have the neck retractile on one side of the carapace, without their having the power of drawing it between their fore feet, and under the buckler and plastron, like the _Cryptoderes_. _Chelys matamata_ (Fig. 38) belongs to this division. This species lives in stagnant water, and is altogether remarkable for its singular appearance--for its depressed, wide, and triangular nostrils, prolonged into a proboscis; its wide gape, rounded jaws, and the cutaneous appendages to the chin. This is sometimes called the Bearded Tortoise. POTAMIANS, OR RIVER TORTOISES. The River Tortoises live constantly in the water, only coming to land occasionally; they swim with much ease below and on the surface. The carapace is very broad and flat; the toes united up to the claws by broad flexible membranes. These membranes change the feet into true paddles, which perform the office of oars. They seem to attain a considerable size, one kept by Pennant for three months weighing twenty pounds, its buckler not reckoned; the neck measuring twenty inches in length. The upper parts of their bodies vary in tint from brown to grey, with irregularly marbled, dotted, or ocellated spots; the underpart is a pale white, rosy, or purple tint. Sinuous brown, black, or yellow lines are symmetrically disposed on the right and left, principally on the neck and on the limbs. During the night, when they think themselves safe, the River Tortoises seek repose on the rocks and islets, or on timber floating in the rivers, from which they plunge into the water on the slightest noise. These Tortoises, which accommodate themselves so perfectly to the medium that they inhabit, are continually at war with the fishes, reptiles, mollusks, and other denizens of the rivers. They are voracious and active, and are relentless enemies to the young of fishes, and especially of Crocodiles.