||Tri*go"ni*a (?), n. [NL. See Trigon. So called in allusion to the triangular shape of some species.] (Zoöl.) A genus of pearly bivalve shells, numerous extinct species of which are characteristic of the Mesozoic rocks. A few living species exist on the coast of Australia.

||Tri*go"ni*a (?), n. [NL. See Trigon. So called in allusion to the triangular shape of some species.] (Zoöl.) A genus of pearly bivalve shells, numerous extinct species of which are characteristic of the Mesozoic rocks. A few living species exist on the coast of Australia.