Conch

n.
  1. (Zoöl.) A name applied to various marine univalve shells; esp. to those of the genus Strombus, which are of large size. Strombus gigas is the large pink West Indian conch. The large king, queen, and cameo conchs are of the genus Cassis. See Cameo and cameo conch.
  2. In works of art, the shell used by Tritons as a trumpet.
  3. (Arch.) See Concha, n.
  4. The external ear. See Concha, n., 2.

The conch is sometimes used as a horn or trumpet, as in fogs at sea, or to call laborers from work.