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. [ 1913 Webster ]

2. (Bot. & Zool.) Having a dull red brick color or a brownish yellow color. [ 1913 Webster ]

Testaceous animals (Zool.), 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. [ 1913 Webster ]