\Tes*ta"ceous\, 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. & Zo["o]l.) Having a dull red brick color or a
   brownish yellow color.

{Testaceous animals} (Zo["o]l.), 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.