The Gastropod Genus Volutocristata Gardner and Bowles (Eocene; California, Mexico): A Synonym of Lyrischapa Aldrich (Eocene; Gulf Coast)

Abstract

The volutid gastropod genus Volutocristata Gardner and Bowles, described from the Eocene of Mexico and California is shown to be a synonym of the monotypic Gulf Coast Eocene genus Lyrischapa Aldrich. As here expanded, the genus Lyrischapa includes at least three species, each of which characterizes middle Eocene strata within a different region of North America: L. harrisi Aldrich, the type species, in the Gulf Coast region of the southeastern United States; L. chiapasensis (Gardner and Bowles), in southern Mexico on the Gulf of Mexico side of the continental divide; and L. lajollaensis (Hanna), on the Pacific Coast. The ancestry and place of origin of Lyrischapa are unknown. The geographic distribution of the genus suggests an immediate center of dispersal in the Caribbean region. It may have evolved in that region or it may be an immigrant from the Tethyan paleobiogeographic province. Dispersal of Lyrischapa to the Pacific Coast was probably by way of a narrow seaway connection across southern Central America or northwestern South America.