Page:The Fauna of British India, including Ceylon and Burma (Reptilia and Batrachia).djvu/28

 Quadrate bone immovably united to cranial arches. Dorsal ribs single-headed, the anterior attached between two vertebra). Body encased in a bony shell. A plastron formed of a small number of elements in addition to the clavicles. No sternum. No teeth ; jaws covered with horny sheaths. Anal opening round or longitudinal. Copulatory organ present, single.

Oviparous ; eggs with a hard shell, except in the Chelonidce.

The Tortoises and Turtles of India fall into five Families*.

Dorsal vertebrae and ribs immovably united and expanded into bony plates forming a carapace. Parietals prolonged downwards towards the pterygoids.

Articulation between the last cervical and the first dorsal vertebra by the zygapophyses only. Marginal bones absent or forming an incomplete series.

Carapace and plastron without epidermal shields, covered with a soft skin Fam. 1. Trionychidae.

Centrum of the last cervical vertebra articulating with the centrum of the first dorsal. A complete series of marginal bones, connected with the ribs.

Digits short ; tail short, with proccelous ver- tebra; Fam. 2. Testudinidae.

Digits short ; tail long ; caudal vertebrae mostly opisthocoelous Fam. 3. Platysternidae.

Limbs paddle-shaped, with only one or two claws. Marine Fam. 4. Chelonidae.

Vertebras and ribs free, separated from a bony exoskeleton. Skull without descending processes of the parietal bones.

Limbs paddle-shaped, clawless. Marine.... Fam. 5. Sphargidae.

Limbs with four or five claws. Tail short Testudinidae. Tail nearly as long as the shell Platysternidae. Limbs with three claws Trionychidae. Limbs with one or two claws Chelonidae. Limbs without claws Sphargidae.
 * These five families, so far as Indian genera are concerned, may be recognized from external characters by use of the following key :