Tail long, covered with rings of shields. Plastron large. Indo-China .......... Platysternidae, p. [345].
Tail short. North and Central America .......... Dermatemydidae, p. [341]. Cinosternidae, p. [342].
Pectoral shields in contact with the marginals.
Plastral shields 11 or 12, without an intergular. Neck retractile in an S-shaped vertical curve .......... Testudinidae, p. [345].
Plastral shields 13, an intergular being present. Neck bending sideways under the shell .......... Chelydidae, p. [399]. Pelomedusidae, p. [390].
Limbs paddle-shaped, with one or two claws .......... Chelonidae, p. [378].
Shell without horny shields, covered with soft, leathery skin.
Digits distinct, broadly webbed, but with only three claws .......... Trionychoidea, p. [404].
Limbs paddle-shaped.
Shell composed of regular series of bony plates. Two claws .......... Carettochelydidae, p. [404].