CHAP. XIX. 



BIVALVES: 

 PINNA; Fin Shell, or Sea-Wing. 



Q. How am I to distinguish the Pinna from 

 shells of a similar description ? 



A. By observing that the shell is sub-bivalve, 

 brittle, erect, gaping, throwing out a beard, or 

 byssus. That the hinge is toothless, and that 

 the valves are united into one. 



Q. Is not the shape of the Pinna a peculiar one ? 



A. It is broad at one end, and gradually tapers 

 towards the other. The valves are convex, equal, 

 and connected on the side of the hinge by a 

 membrane, in such a manner as to form in fact 

 an univalve shell, bearing the appearance of a 

 bivalve. 



Q. Why has the Pinna been termed a marine 

 silk-worm ? 



A. From the extreme fineness of the byssus, 

 which closely resembles silk. Indeed a consider- 

 able manufactory of stuffs, &c. from the threads 

 of the Pinna, is established at Palermo. It is 

 mentioned in the work to which I have so fre- 

 quently referred, that in the year 1754 a pair of 



