PROC. BIOL. SOC. WASH. 96(3), 1983, pp. 349-354 A NEW STROMBINA SPECIES (GASTROPODA: PROSOBRANCHIA) FROM THE TROPICAL WESTERN ATLANTIC Richard S. Houbrick Abstract. — Strombina (Cotonopsis) argentea is the fourth living Strombina species and the first Cotonopsis taxon described from the tropical western At-lantic. It has the most northern distribution of any western Atlantic Strombina species and occurs in deep water. This species is the largest of the four Atlantic taxa, and morphologically resembles the eastern Pacific Strombina (Cotonopsis) deroyae Emerson and D'Attilio, 1969. There is considerable intraspecific varia-tion in axial sculpture. The radula is typically columbellid in form. While processing material dredged by the National Marine Fisheries ship R/V Oregon in deep water near Silver Bank off the north coast of the Dominican Republic, ten specimens of a new, remarkably large Strombina species were recognized. Two were live-collected and contained dried animals, allowing ex-amination of the operculum and radula. The genus Strombina was widespread in the Caribbean during the Miocene, but the diversity of this taxon decreased in the Pliocene. Although there are many species living in the eastern Pacific today, only three Recent species were pre-viously known from the western Atlantic, all from the southern Caribbean, and referred to the subgenus Strombina s.s. This paper describes a fourth Strombina species that is allocated to the subgenus Cotonopsis Olsson, a group previously known only from the Neogene of Central America and the Recent eastern Pacific fauna. The presence of a large, distinctive Strombina living in deep water to the north of the Greater Antilles and Caribbean Sea adds significant dimension to the composition and distribution of this lineage in the western Atlantic. Description Family Columbellidae Strombina Morch, 1852 Subgenus Cotonopsis Olsson, 1942 Strombina {Cotonopsis) argentea, new species Figs. 1-2 Shell (Table 1). — Shell large and slender, fusiform, with elongate tapering spire comprising 10 weakly inflated whorls and ranging in length from 30-43 mm. Whorls sculptured with 19-28 weak slightly curved axial ribs extending length of whorl. Some shells nearly smooth but early whorls of teloconch sculptured with distinct axial ribs. Protoconch large, bulbous, smooth, about Wi whorls. Body whorl large, nearly smooth, round in cross section, slightly angulate at periphery, about one-half shell length. Axial ribs present on anterior of body whorl but fading out near lip. Thick varix just above edge of outer lip. Siphonal constriction of body
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