Article: A new genus of Jurassic bivalve mollusc ancestral to Globocardium

A new genus of bivalve mollusc Cryptocardia is described and assigned to the subfamily Protocardiinae. Four new species are described from the Domerian, Bajocian, and Bathonian stages of Europe, and from the Callovian stage of Africa. This Jurassic genus, characterized by the presence of posterior internal radial ridges and no external radial ornament, is ancestral to the Cretaceous genus Globocardium. A tendency, throughout the Mesozoic, to suppress the internal ridges and to increase the size of shell and coarseness, both of external ornament and internal hinge structure, is established as an evolutionary trend for the two genera. There is no material from the Upper Jurassic or the Caenozoic. A homeomorphous Cretaceous species of Protocardia is described, which departed from the usual subtrigonal outline of Mesozoic Protocardia and converged towards that of Globocardium.