CONCHIFERA. 



299 



the foot is slender, conical, worm-shaped, and produces a 

 silken kind of byssus ; the mouth has two large lips, their 

 inner surfaces beset with blisters ; the mouth tentacles 

 are short, and two on each side are united almost in their 

 whole length ; the gills are generally equal, and half- 

 moon-shaped; near the anal opening in the mantle is a 

 singular conical worm-shaped body, the use of which is 

 doubtful ; adductor muscles two, the front one is tolerably 

 thick, and lies immediately under the bosses, the other is 

 still thicker, rather cylindrical, and almost central. The 

 substance of the shell consists of uprightly placed fibres 

 on the inner surface ; the ligament is linear, and occupies 

 the whole back edge of the shell, and is almost internal. 

 The Pinnacea prefer the seas of warm climates. 



Pinna. Lin. — Shell equivalve, rather triangular, ham 

 or wedge-shaped, very 

 inequilateral ; bosses 

 terminal, the other ex- 

 tremity gaping ; no 

 teeth ; hinge straight, 

 with a long and some- 

 what internal ligament ; 

 shell thin and fragile. Animal, triangular, mantle freely 

 open, no siphons ; mantle margins with cirrhated edges ; 

 mouth with foliaceous lips, and short palpi ; anus furnished 

 with a long ligulate valve ; foot small with a byssal groove ; 

 adductor muscles very unequal.* — About 20 species ; 

 also fossil. 



The Pinna is usually found moored to the sand by its 

 byssus, or Forbes says, lying "with their gaping ex- 

 tremity upwards, and their beaks plunged deep in the 

 ground." It is common to nearly all seas, and grows to a 



* Forbes' s British Moll 



