Trigonia

thumb|right|225px|Diagram of Trigonia costata James Parkinson, showing main morphological features of the shell exterior;a) [[Anterior; p) Posterior; d) Dorsal; v) Ventral; F) Flank; A) Area; c) Costae; mc) Marginal CarinaTrigonia costata ranges from the Lower Jurassic (Toarcian) to Middle Jurassic (Callovian).]] thumb|350x350px|Trigonia sp. from the Jurassic of the Canjuers plateau, Var, France. Max Rouger Collection. Trigonia is an extinct genus of saltwater clams, fossil marine bivalve mollusk in the family Trigoniidae. The fossil range of the genus spans the Paleozoic, Mesozoic and Paleocene of the Cenozoic, from 298 to 56 Ma.

== Description == The genus Trigonia is the most readily identifiable member of the family Trigoniidae, having a series of strong ribs or costae along the anterior part of the shell exterior. They are the first representatives of the family to appear in the Middle Triassic (Anisian) of Chile and New Zealand. The first European examples (Trigonia costata Parkinson) appear in the Lower Jurassic (Toarcian) of Sherborne, Dorset and Gundershofen, Switzerland.