Exogyra are an extinct genus of bivalve mollusks, akin to oysters, from the Jurassic and Cretaceous periods. They have an exceptionally thick pair of shells, the left one of which is coiled whereas the right is flatter. They are supposed to have evolved from a Ceratostreon ancestor.
Transitional Gryphaeate/exogyrate oysters (Bivalvia: Gryphaeidae) from the Lower Jurassic of Northern Chile
Jul 01, 1998; ABSTRACT-Sinemurian and Pliensbachian Exogyrinae from northern Chile described herein as Nanogyra? cf. auricularis are considered...