TESTA'CEOUS, a. [L. testaceus, from testa, a shell. The primary sense of testa, testis, testor, &c. is to thrust or drive; hence the sense of hardness, compactness, in testa and testis; and hence the sense of attest, context, detest, testator, testament, all implying a sending, driving, &c.]

Pertaining to shells; consisting of a hard shell, or having a hard continuous shell.

Testaceous animals are such as have a strong thick entire shell, as oysters and clams; and are thus distinguished from crustaceous animals, whose shells are more thin and soft, and consist of several pieces jointed, as lobsters.

Testaceous medicines, are all preparations of shells and like substances, as the powders of crabs' claws, pearl, &c.