SLIPPER - SnELL. 
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coarsely sculptured . Glyphis densidathrata , 
Eve., is small, white, oval, with tine, close sculp- 
turing. Gadinm radiata, Cpr., has no hole. It 
is circular, low conical, pure white, finely sculp- 
tured, with radiating ribs, and concentric lines 
of growth. Its breadth is one-half of an inch. 
The Slipper-shells are provided with a shelly 
partition, partly shutting off the apex from the 
aperture. We haves two very common species, 
the first of which is Crepidula adunca , Shy., 
Hooked Slipper-shell, Fig. 5, PI. IX. The apex 
is strongly recurved; the aperture is oval and 
variously distorted to fit the surface on which 
the animal roosts. Its color is brown, sometimes 
mottled, with a white partition inside. Its 
length is from one half to a whole inch. It may 
be found between tides, on rocks and shells. 
The White Slipper-shell, Crepidula navicelloides, 
Nutt., is flattened, boat-shaped, with a deck 
hall way across. It is very variable in shape, 
adapting itself to circumstances. Small, smooth 
specimens inhabit dead univalve shells, while 
rough, large ones may be found on the rocks. 
Color, white; length, same as last species. 
Crucibulum spinosum , Shy., 44 Cup and Sau- 
cer Limpet,” is a more southern species. The 
saucer is limpet-shaped, brownish, set with 
many points or spines. Within, instead of a 
deck, as in the last species, is a little triangular 
cup, fastened near the apex. Size, from half an 
inch to an inch and a half. 
Ilipponyx cranioides , Cpr., Fig. 1 , PI. X, 
takes its name from its resemblance in shape to 
a horse’s hoof. The liorse-shoe shaped muscular 
