SLIPPER - SHELL. 37 



coarsely sculptured . Glyphis densidathrata, 

 Rve., is small, white, oval, with fine, close sculp- 

 turing. Gadiniaradiata, 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 ap(x from the 

 aperture. We haves two very common species, 

 the first of which is Crepidula adunca^ Sby., 

 Hooked Slipper-shell, Fig. 5, PI. IX. The apex 

 is strongly recurved; the aperture is oval arid 

 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, Crepidul&navicelloides, 

 Nutt., is flattened, boat-shaped, with a deck 

 half way across. It is very variable in shape, 

 adapting ifself to circumstances. Small, smooth 

 specimens inhabit d^ad univalve shells, while 

 rough, large ones may be found on the rocks. 

 Color, white; length, same as last species. 



Cruc'ibidum spinosum, Sby., ' 4 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. 



IRpponyx cranioides, Cpr., Fig. 1, PI. X, 

 takes its name from its resemblance in shape to 

 a horse's hoof. The horse-shoe shaped muscular 



