title: Trigonia
text: # Trigonia
  
  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.
  
  ## Species
  
  The following Trigonia species have been described:
  
  * T. analoga
  * T. antiqua
  * T. castani
  * T. castrovillensis
  * T. coqueiroensis
  * T. costata
  * T. cragini
  * T. depauperata
  * T. eufaulensis gabbi
  * T. eufaulensis moorei
  * T. guildi
  * T. hemisphaerica
  * T. imbricata
  * T. interlaevigata
  * T. intersitans
  * T. kitchini
  * T. maastrichtiana
  * T. maloneana
  * T. marginata
  * T. mearnsi
  * T. montanaensis
  * T. orientalis
  * T. papuana
  * T. picteti
  * T. plana
  * T. pseudocaudata
  * T. pseudocrenulata
  * T. pullus
  * T. rebouli
  * T. reesidei
  * T. resoluta
  * T. reticulata
  * T. saavedra
  * T. semiculta
  * T. somaliensis
  * T. stantoni
  * T. stolleyi
  * T. suborbicularis
  * T. sulcata
  * T. taffi
  * T. thierachensis
  * T. undulatocostata
  * T. vyschetzkii
  * T. weaveri
  
  ## Distribution
  
  Fossils of Trigonia have been registered in:
  
  ### Permian
  
  Bolivia (Copacabana Formation)
  
  ### Triassic
  
  Austria, China, Italy, the Russian Federation, United States (Alaska, Idaho), and Vietnam.
  
  ### Jurassic
  
  Afghanistan, Argentina, Canada (Alberta, British Columbia, Yukon), Chile, Colombia (Valle Alto Formation, Caldas), 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.
  
  ### Cretaceous
  
  Afghanistan, Algeria, Antarctica, Argentina, Armenia, Australia, Brazil, Bulgaria, Canada (British Columbia), Chile, Colombia (Yuruma Formation, La Guajira, Macanal Formation, Eastern Ranges), 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.
  
  ### Paleocene
  
  Argentina (Cerro Dorotea Formation)
  
  