pinna. 529 



Genus PINNA, Linnaeus. 



Mouth with foliaceous lips. Anus with a long, ligulate 

 valve. 



Shell very oblique, wedge-shaped, triangular, equivalve, 

 exceedingly inequilateral, more or less thin and fragile, 

 gaping posteriorly ; surface of valves smooth, or scaly, or 

 obliquely furrowed, the apical portions sometimes longitudi- 

 nally fissured, the fissure filled with a cartilage; beaks ter- 

 minal. Hinge straight, long, toothless; ligament linear, 

 internal. Pallial impression entire ; muscular impressions 

 very unequal. 



Syn. Chimsera, Poli. Pennaria, Browne. Cyrtopinna, 

 Morch. 



Ex. P. nobilis, Linnaeus, pi. 123, fig. 4, 4, a. 



The structure of the shell in Pinna consists of vertically- 

 disposed fibres on the inner surface. The young shells are 

 very thin and brittle, being composed almost entirely of 

 prismatic cells. Adult shells of some species attain a 

 length of two feet. The nacreous lining of the interior 

 does not extend as far as the ventral margin. The species 

 of Pinna are found in nearly all seas. They range from 

 low-water to sixty fathoms, usually living buried in the mud 

 or sand with the sharp edges of the valves gaping and pro- 

 truding from the surface. Pearls of an amber colour are 

 sometimes found in the shells. Some species are used as 

 articles of food, and others are valued for their long and 

 silky byssus, which, mixed with silk, has been woven into 

 gloves and other articles. 



