172 American Seashells 



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 



