In the four species of marine turtles, the feet are flat and fin-shaped. In one the shell is rather leathery than horny. Some of these marine turtles are carnivorous, living on fish, mollusks, and crustaceans; others are strictly vegetarian, feeding only on roots and various sea-weeds. The flesh of some of the sea turtles is rich and delicious, and a favorite and costly article of food; but of some others the flesh is coarse and strongly flavored, so as to be quite uneatable. The eggs are always sweet, good, and wholesome food. The shell of the sea turtle is a valuable article of commerce, boxes, cases, handles for knives, jewelry and other delicate ornamental things being made from it; it is susceptible of a high polish, which brings out clearly its rich brown and golden shades and markings. Next to the marine turtles, come the fresh-water or river turtles. These eat both animal and vegetable food. They enjoy lying in a bed of mud, their heads lifted above the surface of the stagnant water, their long necks moving snake-like to and fro as they take mouthfuls of air. The fresh-water turtles are generally gregarious in their habits, large numbers of them being found together. They are fond of lying in the sun on logs or banks, near the water, into which they promptly slide at the first hint of danger. They are timid creatures, but if caught will snap and bite furiously. Salt and fresh water terrapins are a variety of turtle. Some scientists distinguish the turtle from the tortoise thus: the turtle is a marine animal, does not hibernate, cannot draw its head and feet inside its shell. The tortoise never goes to sea; can draw itself entirely within its shell, though only the box tortoise can close the shell fast when so withdrawn, and finally, the tortoise hibernates. Some of the best and latest writers on the subject call all these animals turtles, giving the name tortoise to the box tortoise of the wood. Clumsy as turtles appear in their box-like covering, they can walk rapidly on land, are climbers of some distinction, and all of them can swim. The head, neck, and legs of a turtle are of a uniform color,--bronze, blackish green, or deep brown. The shells or boxes are beautifully marked, glossy, ribbed, ridged, or carved, and made up of closely united many-sided plates, fitted upon a thickened, lighter-colored, uniform plate. This shell is not brittle and lime-like, as the shells of mollusks, but is more like horn. In general, the shell or flat covering of the under part of the body is of a lighter color than the upper case, being light brown, yellow, or cream color, with yellow lines dividing the plates, and bordering bands of red, yellow, or purple. The upper shell is usually of a very dark color, marked and lined with darker and lighter tints, and often with a bevelled yellow edge.