Source : Webster's Revised Unabridged Dictionary (1913)

Testaceous \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.