ASTARTID. 233 
VENERICARDIA, Lam., 1801. 
Syn.—Cardiocardita, Blainv. 
Distr—V. planicostath, Lam. (exxiii, 73). 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, radiately costate, covered 
with a rough epidermis; hinge with two robust teeth in the left 
valve, directed obliquely backwards, the posterior one elongated 
and slightly curved; anterior tooth of the right valve rudiment- 
ary. V. borealis, Con. (cxxiii, 74). 3sp. U.S. 
PLEUROMERIS, Conrad, 1867. Shell subtriangular, 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. JV. trv- 
dentata, Say (cxxii, 50). 
Miopon, Carpenter, 1864. 
Distr.—M. prolongatus, Carp. West Coast U.8. MM. orbicu- 
laris, Sowb. (exxii, 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. 
Closely allied to Pleuromeris. 
Proroxkta, 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. 
CaARDITELLA, E. A. Smith, 1881. 
Distr.—3 sp. S. Am. C. pallida, Smith. 
Shell exteriorly 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 minute, placed immediately beneath 
the apex of the valves; pallial line simple. 
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