See text Trigonia is an extinct genus of saltwater clams, fossil marine bivalve mollusk in the family Trigoniidae.

[1] 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.

The first European examples (Trigonia costata Parkinson) appear in the Lower Jurassic (Toarcian) of Sherborne, Dorset and Gundershofen, Switzerland.

Afghanistan, Argentina, Canada (Alberta, British Columbia, Yukon), Chile, Colombia (Valle Alto Formation, Caldas),[3] Egypt, Ethiopia, France, Germany, Greenland, India, Iran, Japan, Kenya, Luxembourg, Madagascar, Morocco, New Zealand, Poland, Portugal, the Russian Federation, Saudi Arabia, Somalia, Spain, Tanzania, Thailand, Tunisia, the United Kingdom, United States (Alaska, California, Idaho, Montana, Nevada, Oregon, Texas, Utah, Wyoming), and Yemen.

Afghanistan, Algeria, Antarctica, Argentina, Armenia, Australia, Brazil, Bulgaria, Canada (British Columbia), Chile, Colombia (Yuruma Formation, La Guajira, Macanal Formation, Eastern Ranges),[4] Egypt, France, Germany, Greenland, Hungary, Italy, Lebanon, Mexico, the Netherlands, New Zealand, Papua New Guinea, Peru, Portugal, Serbia and Montenegro, South Africa, Spain, Switzerland, Tanzania, Turkmenistan, Russian Federation, Ukraine, the United Kingdom, United States (Arizona, California, Delaware, Mississippi, New Jersey, North Carolina, Tennessee, Texas), Venezuela, and Yemen.