PINNA. 



large shells, sometimes exceeding two feet in length; 

 they are for the most part thin, and extremely brittle, 

 being in a great measure formed of perpendicular fibres 

 arranged side by side and adhering very slightly to each 

 other. The shelly plate thus formed is lined with a very 

 thin pearly coat, scarcely extending beyond the muscular 

 impression of the mantle, and consequently only covering 

 the body of the animal, which usually buries itself in the 

 sand or mud about low-water mark, and sometimes in 

 deep water, with the pointed termination of the shell 

 downwards, and fixes itself to pebbles and other sub- 

 stances by means of its long silky byssus, of which each 

 individual possesses a considerable bunch. The byssus is 

 frequently made into gloves and hose, at Naples and at 

 other places on the shores of the Mediterranean, where 

 several species of Pinna are very abundant. 



The species of this Genus are rather numerous, and 

 they are most frequently rough on the outside with irre- 

 gular, pointed, sometimes almost tubular scales, though 

 there are also some species that are nearly smooth: these 

 scales cannot, however, always be depended upon as a 

 specific character, since we have seen several individuals 

 of the same species, one of which is quite rough with 

 muricated spines, another has only a few, and the third 

 is quite smooth. One species, commonli/ called P. saccata,* 

 which, on account of its usual irregnilarity, will not be 

 found to accord well with our character, can, however, 

 only be referred to this Genus, it having nothing to dis- 

 tinguish it except its irregulanty, whiqh is probably 

 caused by the situation it inhabits. 



We believe the Pinnae to be inhabitants of all cU- 

 mates ; several species are common on out coasts and the 

 Mediterranean, the shores of the Atlantic and Pacifiq 

 oceans, as well as those of the East Indies, produce 

 others. We are acquainted with several fossil species, 

 which occur in the secondary and tertiary beds of marine 

 origin : one in particular is beautifully preserved in the 

 indurated sandy bed of London clay, at Bognor; and 

 another is not unfrequently met with in the Calcaire 

 grossier, at Grignon. 



* But not Pinna saccata of Chemnitz. 



