Trigonia
Pronunciation : Tri*go"ni*a
Part of Speech : n.
Etymology : [NL. See Trigon. So called in allusion to the triangular shape of some species.] (Zo?l.)
Definition : Defn: 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.
Source : Webster's Unabridged Dictionary, 1913