Cerion sladeni Pilsbry & Black, 1930

Original Description

"Cerion sladeni new species. Plate 21. fig. 1, a-l.

Andros: Mastic Cay, in Middle Bight. Type No. 152220 ANSP.,para­types No. 152221, collected by Maurice Black.

The shell is perforate, cylindric, convexly tapering in the upper third, white, solid. The whorls are nearly flat, the last produced forward, carry­ing the peristome free. Sculpture: first two whorls are smooth, the next whorl with fine, sharp, somewhat retractive striae. Following whorls are smoothish, but with weak growth wrinkles. The last whorl has rather coarse, irregularly developed ribs on the last half and at the base. The ovate aperture is brown in the throat, and shows a small but rather long parietal tooth and a very small columellar tooth deep within. The peristome is not expanded typically, or is built forward beyond a small expansion.

Length    38 mm., diam. above aperture 15.4 mm. ; 12 whorls. Type, fig. 1c.

    "         45  "          "         "          "       15.5   " ;     14     "

   "       35.5   "         "         "          "       15.5   "

    "         31  "          "         "          "       11.2   "

    "         30  "          "         "          "       14.5   "

Shape and size vary within wide limits as shown in the figures.

Ten percent of the specimens seen from Mastic Cay have the whorls irregularly striped with shades between dilute ocher and carob brown (fig. 1d).

It is named for W. Percy Sladen, former Zoological Secretary of the Linnaean Society of London. This form is evidently closely akin to C. pills­buryi P. & V. of the Bimini Islands, and it might with no great violence he considered a subspecies of that. The shell of C. jenneyi Maynard & Clapp from Anderson Cay in the Berry Island group,³ is indistinguishable from that of C. pillsburyi. This wide distribution of closely related forms appears to indicate that the pillsburyi stock was widely distributed in the Pleistocene when the Andros Bank emerged, and now survives in the places marked in fig. 1 in either identical (jenneyi, travellii) or somewhat altered (sladeni) forms. All of these places would be broadly united across the bank by an elevation of less than three fathoms. According to Daly's views, the ocean level was low enough several times during Pleistocene time for the emergence of a greater bank uniting Andros, New Providence, and Eleuthera. If so, there must have been a general diffusion of the land snails. The group comprising C. sladeni and its allies of the Andros bank cays may be viewed as locally differentiated members of an ancestral stock which spread over the great Pleistocene island, and is elsewhere represented now by C. gubernatoria and C. agassizi on New Pro­vidence and C. eleutherae on Eleuthera. The great extension of Andros west and north doubtless continued long after the connection with islands eastward was interrupted.

            C. sladeni was found in abundance only at Mastic Cay, and everywhere else was distinctly uncommon. At Purser Point it was represented, like C. rhyssum, by a sprinkling of empty shells along the strand line, both species probably having drifted there as dead shells from the region of Northern Bight. C. sladeni probably inhabits an area north of C. rhyssum, for it is quite rare amongst the material collected at Money Cay and High Ridge Cay.

³ Cerion travellii Maynard, from Bridgewater Cay, about 10 miles north of Anderson Cay, does not appear to differ materially from C. jenneyi Mayn." (Pilsbry & Black, 1930:290-292)

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