Webster’s Revised Unabridged Dictionary · 1913
Testaceous
Tes·ta′ceous (tĕs·tā′shŭs), a. [L. testaceus, fr. testa a shell. See Testa.] 1. Of or pertaining to shells; consisted of a hard shell, or having a hard shell.
2. (Bot. & Zoöl.) Having a dull red brick color or a brownish yellow color.
Testaceous animals (Zoöl.), animals having a firm, calcareous shell, as oysters and clams, thus distinguished from crustaceous animals, whose shells are more thin and soft, and consist of several joints, or articulations, as lobsters and crabs.