64 THE ELEMENTS 



Habitation. The Pinnae, which fre- 

 quently grow to a large size, are only 

 found to inhabit the ocean. They are 

 generally found standing erect in the 

 smoother water bays, with the broad 

 end or base of the shell uppermost. 

 And they are sometimes found affixed 

 by their byssus to rocks. 



In Italy the byssus of the Pinna is 

 woven into a sort of silk. The fibres 

 or filaments of which it is composed, 

 are very tough, and of a fine glossy 

 brown colour. The ancient Romans 

 highly esteemed articles made of this 

 byssus ; and at Naples and Palermo 

 there are still manufactories of it. 



This genus forms an excellent inter- 

 mediate link between the bivalve and 

 univalve shells, being in truth what 

 Linne defines it — a sub-bivalve shell ; 

 it being immoveably fixed, by a calca- 

 reous process, at the hinge. 



The Pinnae are wedge-shaped shells, 

 or somewhat of a triangular form, 



