the outside of the body whorl only in the region behind the slightly flaring lip. 3 other cords are present just below the suture. Columella area dished; reinforced by the round, pillar-like columella. A small pimple is present near the posterior canal in the aperture. Outer lip with strong crenulations on the inside. Periostracum a soft gray-black felt. A common littoral species in the West Indies which bears its young in a brood pouch. Rare in Florida.
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Figure 38. Modulus modulus Linné (southeast United States and the West Indies). a, side view of living animal; b, ventral view showing foot, head and under edge of mantle; c, operculum; d, apertural view of shell. X2. (From Abbott 1944 in Johnsonia.)
Family MODULIDAE
Genus Modulus Gray 1842
Modulus modulus Linné
Atlantic Modulus
Plate 21f; figure 38
Florida to Texas and the West Indies.
About ½ inch in length. Characterized by the small, projecting, tooth-like, frequently brownish spine located on the lower end of the columella. Base of shell with about 5 strong, spiral cords. Top of whorls with low, slanting, axial ribs. Color grayish white with beach-worn specimens often exhibiting flecks of purple-brown. Found abundantly among weeds in shallow, warm waters.
Modulus carchedonius Lamarck, the Angled Modulus (Caribbean area) lives in deeper water, and differs in having the periphery of the shell well-angulated, the spiral cords smaller and neater, in lacking the strong, axial ribs, and in never having the columella tooth colored. Not too common.
Family POTAMIDIDAE
Subfamily POTAMIDINAE
(Horn Shells)
Genus Cerithidea Swainson 1840
