CONCHOLOGY. 61 



C. (lepressa. C. bicolor. 



C. sinuata. C concamerata. 



C. citrina. C. aviculina. 



C. orbularis. C. sublevigata. 

 C. lithophagella. 



C. borealis.* C. incrassata.* 



3. Genus Cijpricardia. PI. VII. 

 minimal. As above. 



Shell. Obliquely elongated, equivalve, inequilateral ; valves 

 striated, not ribbed ; distinguished from the Cardita by having 

 three teeth beneath the apices, and a callous lengthened tooth or 

 ridge. Inhabits the coast of Guinea and California. Five living 

 species. Three fossil. 



Cypricardia angulata. Cypricardia coralliophaga. 



C. Guinaica. C. rostrata, 



C. Californica.* 



4. Genus HiateUa. PI. VII. 



Animal. Unknown. 



Shell. Thin, elongated, subrhomboidal, equivalve, very ine- 

 quilateral, gaping at its inferior edge, and at its posterior extre- 

 mity ; summit very anterior, and much flexed to the front ; hinge 

 formed of a single tooth upon one valve corresponding to an 

 emargination in the opposite valve, or of a small tooth with a 

 cardinal pit upon each valve ; ligament exterior and dorsal. In- 

 habits the British seas. Two species. 



Hiatella Arctica. Hiatella biaperta. 



5. Genus Isocardia. PI. VIII, 

 Animal. Body very thick : edges of the mantle finely papilla* 

 ceous, separated inferiorly, and united behind by a transverse 

 band, pierced with two orifices surrounded with radiating papillae ; 

 foot small, compressed, trenchant. 



Shell. Free, regular, inflated, equivalve, very inequilateral, 

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