66 BIVALVES PINNA. 



ingly brittle or fraoile in subslaiice, and almost invaria- 

 bly gape atone end. Tiic greatest })ortion of the Pinnae 

 have longitudinal ribs, and on them arc placed elevated 

 transverse strioe, often terminating in imbricate arched 

 scales, and prominent canaliculate tubular spines. 



Such is the case vvi<h the Pinna rudis and mm-icata: 

 in the younger shells of these two species, the spines ap- 

 pear but as minute prickles. In other specimens, as the 

 Pinna saccata (satchel), &c. &c.'the ribs are not so ar- 

 ticulate, but more undulate, and are perfectly free from 

 scales or spines* The colors of Pinni]e admit of some va- 

 riation, though they usually have a horn-like appearance, 

 which is often overcast with a steel-blue or copper-colored 

 gloss. The hinge of the Pinnse is invariably without 

 teeth, notwithstanding which, the valves adhere so close- 

 ly in the region of the beaks, that they appear as if unit- 

 ed in one. There are some of the young shells of this 

 genus that do not exceed an inch in length, whereas 

 some of the adults grow to n.ore than three feet. 



This genus is famous for producing a very fine sort of 

 byssus or beard, which itatfordsin large quantities; and 

 the Italians frequently convert it into sundry articles of 

 wearing apparel, which in appearance vie with the finest 

 silk. These shells are usually found in smooth water and 

 bays, with the smaller end sticking in the mud or sand, 

 and the wide end somewhat open. The animal, in some 

 instances, is accounted excellent and luxurious food. 



The Mediterranean produces Pinnaj in great number: 

 they are also to be found in the Indian, American, At- 

 lantic, and European oceans. The Adriatic and Red seas 

 also supply some species. The Pinna, probably, derives 

 its name from its resemblance to a wing, or fin of a fish. 



