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.

Source: Webster's Revised Unabridged Dictionary (1913)