SLIPPER - SHELL. 61 



coarsely sculptured. Glyphis densiclathrata, 

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

 turing. Gadinia radiata, Cpr., lias 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 ape x from the 

 aperture. We haves two very common species, 

 the first of which is Orepidula adunca, Sby., 

 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, Crepidulw navicclloides, 

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

 halt way across. It is very variable in shape, 

 adapting itself to circumstances. Small, smooth 

 specimens inhabit doad univalve shells, while 

 rough, large ones may be found on the rocks. 

 Color, white; length, same as last species. 



Crucihulum sjpinosurn, Sby., 4i 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. 



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

 takes its name from its resemblance in shape to 

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



