Page:American Seashells (1954).djvu/410

328 Cadulus quadridentatus Dall Four-toothed Cadulus Figure 69b North Carolina to both sides of Florida and the West Indies. 5 to 10 mm. in length, swollen behind the aperture. Apex with 4 well- defined slits. In cross-section the shell is roundish. Commonly dredged from 3 to 50 fathoms. Subgenus Gadila Gray 1847 Cadulus mayori Henderson Mayor's Cadulus Southeast Florida. 3 to 4 mm. in length, swollen just anterior to the middle of the shell. Apical opening % the size of the aperture and usually has i or 2 callus rings within the opening. Fairly common from 1 6 to 1 00 fathoms. family DENTALIIDAE Shell with the greatest diameter at the aperture. Foot conical and with epipodial processes. Median tooth of the radula twice as wide as long. Genus Dentalium Linne 1758 The shell is an elongate, curved tube open at both ends, and somewhat resembles an elephant's tusk. The diagnostic characters are the type of sculp- turing (ribs, riblets and circular threads or incised lines), the form of the apex, the degree of curvature, the size and thickness of shell and the position and form of the apical slit. The ten or so subgenera are nebulous in charac- ter and definition and one should consult the works of J. B. Henderson, H. A. PUsbry and W. H. Dall. Subgenus Dentalium s. str. Dentalium laqueatum Verrill Panelled Tusk North Carolina to south Florida and the West Indies. I to 2/4 inches in length, thick-shelled and dull-white in color. Apex sharply curved; anterior % of shell slightly arched. 9 to 12 strong, elevated, primary longitudinal ribs with equally spaced, concave intercostal (space between ribs) spaces. Ribs fade out at the anterior third. There are fine reticulations over the entire shell. A supplemental tube is present in the young shells. Abundant in sandy mud from 4 to 200 fathoms.