ABSTRACT:A new genus of Late Cretaceous (Santonian-early Maastrichtian) ostracodes, Bicornicythereis, is described, based on the following species that occur in the U.S. Coastal Plain: B. bicornis (Israelsky), B. communis (Israelsky), B. levis (Crane), B. nodilinea (Crane), B. polita (Crane) and B. veclitella (Crane). One species included in the new genus, B. communis, was assigned to the genus Curfsina formany years. Analysis of themuscle scar patterns of that species and of species assigned to Curfsina in Europe, South Africa and Australia indicates that, although similar externally, the species evolved from pre-existing species in each region, and therefore should not be assigned to the same genus. The paleobiogeographic pattern of benthic ostracodes, particularly where faunal barriers are widely recognized to exist, is emphasized as crucial during phylogenetic analysis.