"Cerion (Umbonis) sisal, new species

Plate 57, fig. 3

Description.  Shell about 32 mm. (11 inches) in length, cylindric, with a short tapering spire, rather heavy in structure and strongly sculptured. Color a dull light-gray, the costae being the same color. Whorls 11, slightly convex, the nuclear whorls opaque, somewhat glass-like in appearance and faintly axially costate. Spire extended, parallel-sided for about four whorls above the aperture, then conic to the summit. It is produced at an angle of about 80°. Aperture subquadrate in outline and somewhat flaring. Outer lip reflected. Parietal ridge well­developed making the aperture holostomatous. Parietal tooth centered, small and short. Columellar tooth small and rela­tively inconspicuous. It extends backwards for about one whorl. Columella short and nearly straight. Umbilicus rimate and rather shallow. Suture moderately impressed. Sculpture consisting of numerous, somewhat irregular, robust, axial cos­tae which number 13 to 17 on the body whorl. Spiral sculp­ture consisting of numerous deeply incised lines or threads which are cut into the shell even over the axial costae. In the present series which were collected alive, there is no trace of the powdered element nor the tendency to agglutinate minute sand grains to the shell.

            length               width                whorls

              32                    14 mm.              11          Holotype

              32.5                 14                     11          Paratype

              31.5                 13.6                 11                 "

              29.5                 14                     11                 "

Types. Holotype, Museum of Comparative Zoölogy, no. 181992, from east side Boca de Mosquito, Mariel, Pinar del Rio, Cuba. Aguayo, Clench, Howell and Turner collectors, June 1949 and again in July 1950. Paratypes in the Museum of Comparative Zoölogy, Museo Poey, United States National Museum and the Museum of Zoölogy, University of Michigan."

Remarks. This species is remarkably uniform in both shape and size. It is very possible that it is a hybrid element which has reached some sort of stability in both form and structure. The differences are rather marked between this form and johnsoni which exists on the opposite side of Boca de Mosquito. It is possible that repeated introductions of johnsoni have brought about profound changes in the original Cerion stock at this limited locality. To the east of Boca de Mosquito the johnsoni characters become less and less pronounced, partic­ularly in the reduction and extent of the incised lines and the less straight-sided appearance of the early whorls." (Clench & Aguayo, 1952:427-428).