Cerion (Umbonis) rehderi, new species

Plate 57, fig. 2

Description.  Shell cylindric, rather small, reaching 16 mm. (a little over ½  inch) in length, rimately perforate and finely costate. Color a dull uniform gray, interior of aperture being a dull, creamy-brown. Whorls 9 to 10 and slightly convex. Spire extended, last 4 whorls nearly straight-sided, early 5 whorls forming a slight convex cone, the conic portion forming an angle of about 45°. Aperture subquadrate. Outer lip reflected but not turned backward. Columella short and straight. Pari­etal tooth centered, low and short. Columellar tooth low and extending back for nearly a full whorl. Umbilicus rimate, small and shallow. Sculpture: first 2 whorls glass-like and smooth, remaining whorls finely and axially costate, the costae num­bering 20 to 25 on the body whorl. Spiral sculpture consisting of numerous and fine incised lines which do not cut into the crests of the axial costae. These spiral lines are generally finely powdered. There are a few agglutinated sand grains.

            length               width                whorls

            26.3                 5.9 mm.            10                    Holotype

            24.7                 6.1                   9                      Paratype

            23.5                 5.9                   9                      Paratype

Types. Holotype. Museum of Comparative Zoölogy, no. 189032, from Jackline, 1 mile west of Conch Shell Point, Great Inagua, Bahama Islands.

Paratypes, Museum of Comparative Zoölogy, no. 189033; Museo Poey, Universidad de la Habana; United States National Museum; and the Academy of Natural Sciences, Philadelphia, from the same locality.

Remarks.  In relationship, this species is nearest to C. acuticostatum Sanchez Roig from Cayo Mégano Grande, Camagüey, on the north coast of Cuba. It differs from this species in being far less conic (from the body whorl), and by possessing more numerous costae. It does not appear to be closely related to C. turnerae Clench and Aguayo from the north coast of Great Inagua. This last species is a little smaller, has more globose whorls and much fewer costae.

   C. rehderi, so far as now known, is limited to this single locality on the south shore of Great Inagua. It was found as­sociated with C. dalli Maynard, with no indication of any hy­bridization between the two species. In fact, this is one of the few known cases in which two separate elements of Cerion are known to exist in the same area without crossing.

   This species is named for H. A. Rehder, Curator of Mollusks in the United States National Museum.