Chelonia

Chelonia, an order of Reptiles (q.v.), dating from the Trias, and containing the Turtles and Tortoises (see these words). The order, which is very widely distributed, includes marine, freshwater, and terrestrial forms. The body is enclosed in a kind of case, consisting of two shields closely united at the edges, except at the openings for the head, limbs, and tail, which are more or less retractile. The upper shield is known as the carapace; the lower as the plastron. Four limbs are always present. There are no teeth, and the jaws are cased in horn so as to form a kind of beak.