CONCHOLOGY. 75 



3. Pinna. The Wing Shell. Fifteen species. 

 This genus is the same as constituted by Linnaeus ; the 

 shell is marine, generally very brittle and fragile, in form re- 

 sembling an acute angled triangle ; usually covered with lon- 

 gitudinal ribs and elevated transverse striffi ; generally horn 

 coloured. 



This genus is remarkable for the production of an abun- 

 dant byssus of a fine brown silky texture, which the Ital- 

 ians frequently fabricate into articles of dress, equal in ap- 

 pearance to the finest silk. 



The Pinnae often grow to a large size ; they are some- 

 times found standing erect in the smooth-water bays, with 

 the base of the shell uppermost, but generally affixed by the 

 byssus to rocks and other sub-marine bodies. The fila- 

 ments that compose the byssus are so tough and strong that 

 the shells are not easily detached. 



Shell fibrous, fragile, regular, equivalve, longitudinal, tri- 

 angular, base gaping and as if truncated ; summit pointed 

 and straight ; hinge dorsal, longitudinal, linear, and without 

 teeth; marginal ligament occupying almost the whole of 

 the dorsal edge of the shell ; one very broad muscular im- 

 pression behind a trace of the anterior in the summit. 



Pinna rudis. Pinna muricata. 



P. flabellum. P. pectinata. 



P. seminuda. P. saccata. 



P. angustina. P. varicosa. 



P. nobilis. P. dolabrata. 



P. squamosa. P. ingens. 



P. marginata. P. vexillum. 



P. nigrina. 



P. squamosa. The scaly Pinna. 



Species very close and rounded at the posterior extremity ; 

 valves convex, covered with vaulted imbricated scales. 



P. flabellum. The fan Pinna. PI. 13, fig. 2. 



Species gaping at the posterior extremity, which is as if 



