CHAPTER II.
TORTOISES AND TURTLES.
The order of the Chelonians, including the Tortoises, Turtles, and Terrapins, with their allies, constitutes one of the most distinct and readily defined groups of the Reptile Class. The more or less complete bony shell, or carapace, which encases the body, and into which both head and limbs can in many cases be completely retracted, separates these reptiles very widely from the other orders. In some respects certain details of the skull-structure assimilate them to the Crocodiles; but here again there is an entire absence of the rows of formidable teeth, the upper and lower jaws being sharply pointed, covered with horn, and thus converted into a trenchant beak. The two leading groups of the Tortoises and the Turtles are distinctly separated, by the respective conformation of their limbs, for a terrestrial or aquatic existence. The Tortoises have normal walking-legs, with toes and, in most instances, claws, fitting them for walking on the land or burrowing into the earth. In the True Turtles these limbs take the form of flattened paddles, and in no instance are more than two of the toes provided with claws.
The Tortoises are sub-divided by zoologists into some six or eight subordinate groups or families, for the most part distinguished by the respective modifications of their protective shells. This shell in all tortoises and turtles consists of two essential elements—the upper or back casing, known as the "carapace," and the under one, or so-called "plastron," which covers the ventral surface. In some forms these two elements are completely welded into one another, forming a continuous box-like shell; in others they are more or less separate; while in yet another series the lower shell is rudimentary. These distinctions have been found to constitute a convenient basis for classification.
Photo by C. N. Mavroyeni] [Smyrna.
ASIATIC TORTOISES.
A tortoise, like a turtle, turned over on its back, represents one of the most helpless of living animals.
In the True Land-tortoises, which invite first attention, the upper and lower shells are completely united in a box-like form, and the neck, bent in the form of the letter S, can be completely retracted within it. The limbs are club-shaped, covered with horny scales or tubercles, and adapted for walking, the toes being unwebbed, and provided with strong claw-like nails.