Page:American Seashells (1954).djvu/115

Rh 1 to 2 inches in maximum diameter. Similar to D. cayenensis but differs in that: (1) every second radial rib is larger; (2) concentric threads are more distinct and, by crossing the ribs, form little squares; (3) radial ribs often have nodules or scales. Color usually white, cream or gray, sometimes with obscure radial bands. Intertidal. Common in the West Indies.

$1/2$ inch in maximum diameter, rather thin, depressed. Apex at anterior third of shell. Base elliptical, raised slightly at the center, so that the shell rests on its ends. Short front slope slightly concave, back slope convex. Orifice narrow and trilobated. Exterior shiny, with numerous, finely beaded radial ribs. Color white, with many of the ribs entirely or partly blackened. Margin very finely crenulate. Internal callus around hole frequently bounded by a black line. Not very common. Dredged 6 to 72 fathoms, but has been picked up on beaches. Do not confuse with D. dysoni which is more likely to be encountered, especially at Sanibel Island.

$1/2$ to $3/4$ inch in maximum diameter, depressed and with straight sides. Base ovate. Apex slightly in front of the middle and characterized by a blunt knob situated behind the posterior wall of the small, almost triangular orifice. Sculpture of 18 strong ribs with three smaller ones between, and with numerous concentric lamellae. Color milky-white or cream with 8 solid, broken or dotted black rays. Margin sharply crenulated with the denticles arranged in groups of four. Distinguished from cayenensis by the shape of the orifice. Moderately common, sometimes washed ashore.

$1 1/2$ to $2 1/2$ inches in maximum diameter, slightly less than $1/3$ as high. The roundish to slightly oval, flat-sided apical hole is $1/11$ the length of the shell and about $1/3$ back from the narrow, anterior end of the shell. Sculpture of coarse radial and weaker concentric threads. Color externally is grayish white with about 12 to 18 irregularly sized, purplish blue, radial color bands. Commonly found clinging to rocks at low tide. In the south, dredged no deeper than 20 fathoms, and often found on the stems of kelp.