Source : Webster's Revised Unabridged Dictionary (1913)

Pentamerus \Pen*tam"e*rus\, n. [NL. See {Pentamerous}.]
   (Paleon.)
   A genus of extinct Paleozoic brachiopods, often very abundant
   in the Upper Silurian.

   {Pentamerus limestone} (Geol.), a Silurian limestone composed
      largely of the shells of Pentamerus.