Gigantostrea
Gigantostrea is an extinct genus of marine bivalve mollusks belonging to the family Gryphaeidae. This genus is known in the fossil record from the Eocene to the Miocene (age range: from 48.6 to 15.97 million years ago). These fossils have been found in Europe and United States. Description. Shells of "Gigantostrea" can reach a size of about . These fossil shells are brittle, inequivalve, with the lower valve convex and the upper valve flat or slightly concave. The lower valve was cemented to the substrate. Species. Species within this genus include: