MOLLUSC A OR UNIVALVES. 151 



the Patella; but none are so beautiful as those 

 which are found in the Tropics. 



24. Crepidula. — Shell irregular in shape, 

 and often very much flattened ; the inside 



with eyes at the base ; 

 foot small. — There are 25 recent species*, and 

 1 fossil. 



This is a curious and often a very beautiful 

 shell. The Crepidula Onyx is of the most bril- 

 liant black in the inside, with the little half- 

 deck, as it may be called, of a beautiful white, 

 and having the margin of the shell tinged with 

 a rich brown. These shells are found on rocks, 

 and are often of a very irregular outline at 

 the circumference ; like the Patella, they con- 

 stantly remain upon the same portion of rock, 

 and form the margin to agree with its shape. 



* Several of the recent species are also found in a 

 fossil state. 



h 4 



