304 



POPULAR CONCHOLOGY. 



length, thickened at their edges, and beset with small 

 tentacles : on each side are a pair of large, tolerably equal, 

 half-moon-shaped gills, which are not connected with 

 those on the side ; the mouth is oval, and large, with two 

 rather large lips, beset inside with fleshy lamillas, which 

 on each side extend beyond the lip tentacles; these are 

 short, broad, and at their free ends obliquely truncated ; 

 the foot is small, worm-shaped, and bears a coarse byssus, 

 the filaments of which in some, resemble those of the Area, 

 growing together in a mass. The shell is equivalve, 

 wing or leaf-shaped, iridescent, the hinge edge forms a 

 straight line, before and behind prolonged into ears ; with 

 a notch in the right valve for the passage of the byssus. 

 The Malleacea live almost exclusively in the seas of the 

 Torrid Zone, and in the early periods of the creation have 

 been much more numerous than at present. 



Avicula. Brug. — Shell inequilateral, inequivalve, 

 transverse, irregular ; 

 hinge margin straight 

 and much lengthened, 

 ears unequal, no teeth, 

 byssus large, passing 

 through a notch in the :^^ s> ^^ 

 valves; exterior folia- Aviculd 

 ceous, inside of a bril- 

 liant pearly substance; muscular impressions two or 

 more, one larger than the others ; pallial entire. Animal 

 shaped like the shell, its mantle freely open, with cir- 

 rhated margins ; no siphons ; foot small, cylindric, fur- 

 nished with a byssal groove ; palpi large ; adductor 

 muscles* very unequal, one being greatly larger than the 

 rest. | — About 30 species; also fossil. 



* Philippi considers these as one. 



t Forbes's British Moll. 



