n. The shell of a turtle or tortoise; specifically, the upper shell, the under shell being called the plastron.n. In Mammalia, the shell of an armadillo.n. In Cirripedia, the multivalvular shell, test, or case.n. In higher Crustacea, the shield covering the cephalothorax, sometimes separable into a cephalostegite and an omostegite. See cut under Apus.n. One of the many hard cases, tests, or shells which are likened to a carapace, as those of certain infusorians; a lorica.