AST ART ID^. 233 



Yenericardia, Lam., 1801. 



Syn. — Cardiocardita, Blainv. 



Distr. — V. planicostata^ Lam. (cxxiii, 13). Fossil ; Cret., 

 Tert. 



Shell suborbicular, inequilateral, radiately ribbed ; hinge with 

 two oblique cardinal teeth, and no laterals. 



Animal locomotive, with a sickle-shaped foot, like Cardium. 



CYCLOCARDiA, Con., 1867. Rounded, radiatel}^ costate, covered 

 with a rough epidermis ; hinge with two robust teeth in the left 

 valve, directed obliquelj^ backwards, the posterior one elongated 

 and slightly curved ; anterior tooth of the right valve rudiment- 

 ary. V. horealis^ Gon. (cxxiii, 74). 3 sp. IT. S. 



PLEUROMERis, Conrad, 1867. Shell subtriangnlar, radiately 

 ribbed, hinge in the right valve with one broad, furrowed, 

 recurved tooth, in the left valve with three teeth, the anterior 

 one small and fitting into a cavity in the opposite valve. V. tri- 

 deyitata, Say (cxxii, 60). 



MiODON, Carpenter, 1864, 



Distr. — M. prolongatus, Carp. West Coast U. S. M. orbicu- 

 laris, Sowb. (cxxii, 52-54). Oolite ; England. 



Shell ovately subtrigonal, small, solid, ventrally much produced, 

 with the umbones situated anteriorly, radiately ribbed, the ribs 

 being partially intersected by concentric sulcations ; hinge in the 

 right valve with one posterior cardinal and one anterior lateral 

 tooth, left valve with one triangular anterior and one elongated 

 posterior cardinal, and a very small anterior lateral tooth. 

 Closel}^ allied to Pleuromeris. 



Prorokia, Boehm, 1883. 



Distr. — Fossil, 4 sp. P. ( Cardita) ovalis, Quenst. 



Shell small, long-ovate, equivalve, very inequilateral, beaks 

 slightly curved, anterior; surface concentrically striate ; inner 

 margin thickened and crenulated ; teeth 1'2, with a slightly 

 developed posterior lateral and a still smaller anterior lateral ; 

 anterior impression linear, deep, surrounded by a peculiar 

 swelling, posterior impression on a raised plate. 



Carditella, E. a. Smith, 1881. 



Distr. — 3 sp. S. Am. C. pallida, Smith. 



Shell exteriorl}-^ like Cardita ; hinge composed of two cardinal 

 teeth in the left valve and one in the other ; each valve has also 

 two lateral teeth, one nearly marginal on the one side, the other 

 on the opposite side being well within the outer edge, with, a 

 groove between it and the margin for the reception of the sub- 

 marginal tooth of the other valve ; external ligament small, yet 

 distinct ; internal cartilage miniite, placed immediately beneath 

 the apex of the valves ; pallial line simple. 

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