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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. Unionida. Shell oblong, hinge toothless 

 or with large lateral teeth. Mantle lobes free 

 all round. 



Fam. 3. Driessenadce. Shell triangular, hinge 

 toothless. Mantle lobes united, pierced with 

 three holes. 



Fam. 1. CYCLAD^E. 



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. 



