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Class II. CONCHIFERA Lam. 



The animals without any distinct head, the mouth 

 being situate between the four leaf-like lips, with 

 a more or less distinct, compressed, central foot, 

 enveloped by the two pair of leaf-like gills and the 

 large leaf-like mantle, which are covered by two 

 shelly valves, which are united together by a ligament 

 along their dorsal edge. 



These animals are all aquatic and mostly marine ; 

 the British fluviatile species belong to one section and 

 three families, viz : 

 I. Dimyaria. Shell oblong-longitudinal ; animal with 



an anterior and posterior subequal adductor muscle. 



Fam. 1. Cycladce. — Shell ovate, hinge with two or 

 three diverging teeth. Mantles, lobes free be- 

 neath. 



Fam. 2. Unionidce. — Shell oblong, hinge toothless 

 or with large lateral teeth. Mantle lobes free 

 all round. 



Fam. 3. Driessenada. — Shell triangular, hinge 

 toothless. Mantle lobes united, pierced with 

 three holes. 



Fam. 1. CYCLADiE. 



Animal — the mantle lobes free beneath and in 

 front, united behind, and extended into one or 

 two siphons; foot compressed, subquadrate, or 

 becoming strap-shaped. 



Shell subcordate, porcellanous, thin, covered with a 

 hard olive horny periostraca, hinge teeth two or 

 three, diverging; lateral teeth distinct, laminar. 



