'74 BIVALVES.— PINNA. 



brittle or fragile in substance, and almost invariably gape 

 at one end. 



The greatest portion of the Pinnae have longitudinal ribs, 

 on which are placed elevated transverse striae, often ter- 

 minating in imbricated arched scales, and prominent ca- 

 naliculated tubular spines; the P. rudis and P. muricata 

 may be adduced as examples : in the younger shells of 

 these two species, the spines appear only as minute 

 prickles. In other specimens, as the P. saccata (satchel), 

 Szc. the ribs are not so articulate, but are more undulated, 

 and perfectly free from scales or spines. 



The Pinnae have usually a horn-like appearance, which 

 is often overcast with a steel-blue or copper-colovn-ed gloss. 

 The hinge is invariably without teeth ; the valves never- 

 theless adhere so closely in the region of the beaks, that 

 they appear as if united together. 



Some of the young shells of this genus are less than an 

 inch in length, but the adults often exceed three feet. 



This genus produces, in large quantities, a very fine sort 

 of byssus or beard, which the Maltese frequently convert 

 into sundry articles of wearing apparel, vieing in appear- 

 ance with the finest silk. 



The Pinnae are usually found in smooth water and bays, 

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

 wide end a little open. The animal, in some places, is ac- 

 counted excellent food. 



The Mediterranean produces Pinnae in great number: 

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

 tic, and European oceans; as well as in the Adriatic and 

 Red seas. 



The Pinna, probably, derives its name from its resem- 

 blance to a wing or fin of a fish. 



