54 CONCHOLOGY. 



teeth in each valve, turned in the same direction. Five living 

 species. Ten fossil species. 



Venericardia Australis. Venericardia flammea. 



V. imbricata. V. Tankervillii. 



V. crassicosta. 



CoxcHiE Flttviatiles. Three Genera. 



5. Genus Cyclas. 



Animal. Body oval, thick ; edge^ of the mantle simple ; tubes 

 short and united ; foot v^^ide, compressed at base, and terminated 

 by a sort of leg or appendage. 



Shell. With an epidermis, oval, or sub-orbicular, regular, equi- 

 valved, inequilateral ; summits obtuse, contiguous or turned 

 anteriorly ; hinge similar, complex, formed by a slightly variable 

 number of cardinal teeth, and by two separated lateral teeth with 

 a pit at the base ; ligament exterior, posterior, and inflated ; two 

 distant muscular impressions, united by a faintly marked abdomi- 

 nal band, and without posterior excavation. Eleven'species. 



Cyclas cornea. Cyclas rivicola. 



C. obliqua. C. lacustris. 



C. obtusahs. C. calyculata. 



C. Australis. C. fontinahs. 



C. striatina. C. sulcata 



*C. Sarratogea. 



6. Genus Cyrena. 

 Animal. As above. 



Shell. Rounded and trigonal, ventricose, inequilateral ; hinge 

 with three teeth on each valve ; two lateral teeth, one of which is 

 near the primary ones ; ligament exterior, situated on the largest 

 side. The apices are always eroded or carious in shells of this 

 genus. Inhabits the rivers of China. Ten living species. One 

 fossiL 



Cyrena orientalis. Cyrena trigonella. 



C. depressaji C. cor. 



