Page:American Seashells (1954).djvu/222

172 I to 2 inches in length, fairly thick-shelled, characterized by its glossy, dark-chocolate to whitish brown interior, and by the large, slightly concave, pure-white deck inside which has a sinuate free edge. Very common from shallow estuaries to 50 fathoms on rocks, on other shells, or stacked up on top of each other. Crepidula excavata Broderip Excavated Slipper-shell Monterey, California, to Peru. I inch in size, rather thin; back strongly arched with the apex distinct and hooked under itself near the posterior margin of the shell. Characterized by its light brownish white color, by the straight or slightly curved edge of the interior deck, and by a weak muscle scar on each side just under the deck. Found commonly attached to rocks and other shells. Subgenus Janacus Morch 1852 Crepidula plana Say Eastern White Slipper-shell Canada to Florida and the Gulf States. Rare in the West Indies. 34 to I % inches in size, very flat, either convex or concave, and always a pure milky white. The apex is very rarely turned to one side. It commonly attaches itself to the inside of large, dead shells, and rarely, if ever, "piles up" like fornicata. A common shallow-water species. Crepidula ninmnaria Gould Western White Slipper-shell Alaska to Panama. % to I ^ inches in length, characterized by its glossy-white underside, flattened shell, large deck which usually has a weak, raised ridge (or some- rimes a hint of an indentation) running from the apical end forward to the leading edge. Exterior with or without a yellowish periostracum. Found in rock crevices and apertures of dead shells. Super fajmly STROMBACEA Family XENOPHORIDAE Genus Xenophora Fischer von W. 1807 This group of gastropods is noted for its peculiar habit of cementing to its own shell fragments of other shells, stones, bits of coral and coal. The animals resemble those of the Strombus conchs, but the operculum is much wider and not sickle-shaped. B. R. Bales once humorously observed: i