NEW GENERA OF CENOZOIC MURICID GASTROPODS, WITH COMMENTS ON THE MODE OF FORMATION OF THE LABRAL TOOTH

Analysis of previously unstudied shell characters reveals the existenc e of three new genera of Cenozoic muricid neogastropods. These are the new genera Muregina (type species: Murex lugubris Broderip, 1833; ?ea rly Miocene, Pliocene to Recent, eastern tropical Pacific); Kestoceneb ra (type species: Murex curvicosta Grateloup, 1840; early to late Mioc ene, Europe); and Edithais (type species: Concholepas drezi Vokes, 197 2; early to late Miocene, circumtropical). A review of muricids with a labral tooth (a ventrally directed projection on the outer lip) shows that this structure forms in several distinct ways. It may form at th e end of an external groove (as in Muregina) or cord (as in Kestoceneb ra), grow continuously or discontinuously, and lie at positions rangin g from the upper end of the siphonal canal to just below the middle of the outer lip. The labral tooth evidently evolved independently sever al times, often quite recently in genera such as Muregina, in which ol der representatives lack a labral tooth.