Cerion caminus Gould, 1984

Original Description

     Cerion caminus is the first member of the distinctive subgenus C. (Umbonis) found on Eleuthera (modern species inhabit several islands of Great Bahama Bank, see Woodruff and Gould [1980]).  It is the only known fossil Umbonis in the Bahamas and establishes the antiquity of dispersal routes that have brought populations of this subgenus to so many Bahamian Islands (presumably from Cuba).  It has been found in stratified white-soil deposits and directly in eolinites of two adjacent Pleistocene dunes, probably representing the 120,000 B.P. high stand, on central Eleuthera (localities 61 and 64 of Gould and Woodruff).

     Cerion caminus exhibits all the distinctive Umbonis characters, though often in muted form and not on all specimens.  (This suggests that it may have been undergoing hybridization with another species, perhaps of the mottled morphotype.  This is a common situation in Cerion, and many Umbonis populations, including C. felis on Cat Island, C. glans irregulare on Andros, and C. blandi on Salt Cay, are now being effaced by hybridization.)  Ribs are strong and wavy, as in "classical" Umbonis, the aperture is rounded but somewhat wavy and irregular in its outer border; the lip of the aperture is wide but unreflected.  Only 2 of 15 specimens show clear traces of the incised spiral lines that form the most distinctive character of C. (Umbonis).

     The shells of C. caminus are solid, light brownish-red in color, though the ribs are white (a common circumstance in Cerion).  The initial whorls are small and placed below the protoconch, forming a triangular apex with slightly bulging sides.  Whorls continue to expand in width at an only slightly decreasing rate throughout ontogeny producing the triangular form often found in Umbonis and muting the transition between allometric phases 1 and 2. As a smokestack dwarf, the triangle of C. caminus is relatively narrower than in any Umbonis of normal size and triangular outline, C. johnsoni of Cuba and C. stevensoni of Long Island, for example. (See main body of paper for why Umbonis dwarfs of triangular outline, given general rules of growth within Cerion, have higher spires than their counterparts of normal size.)  The aperture is rounded, placed under the last whorl, and accordant in direction of growth with the previous whorls.

     Cerion caminus is a small, high-spired Umbonis, a smokestack dwarf in the terminology of this paper.  Its paratype sample, the only one with sufficient specimens for measurement (Fig. 14), averages 8.46 ppostprotoconch whorls, and exhibits mean values of 23.34 mm in height and 7.15 mm in width for an average shape (height / width) of 3.26, far in excess of any larger Umbonis.

     Derivatio nominis. - From Latin, caminus, a chimney, in reference to its status as a smokestack dwarf.

     Temporal and geographic distribution. - Known only from two adjacent Pleistocene dunes on central Eleuthera, localities 61 and 64 of Gould and Woodruff.  The only Bahamian Umbonis of reasonable similarity with C. caminus is C. acuticostata from Cuba.  But all the characters held in common (triangular cross-section, strong ribs and rounded, wavy and unreflected aperture) are primitive for the subgenus, and not synapomorphic signs of close relationship.  The cross-section of C. acuticostata is almost perfectly triangular, while that of C. caminus bulges slightly at the sides since the shell is somewhat domed in shape.

     Holotype (Fig. 14).  Deparment of Invertebrate Paleontology, Museum of Comparative Zoology, Harvard University, No. 29183, Locality 61 of Gould and Woodruff, Pleistocene of Eleuthera.  Height 26.1 mm, width 7.8 mm, 9⅛ whorls."  (Gould, 1984:194)

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