CYRENIDA. 185 
tooth in each valve; pallial sinus shallow. Perhaps scarcely 
subgenerically distinct from Cyrena. For a doubtfully creta- 
ceous species. D. tenuis (exv, 32). 
IsopoMA, Desh. Shell thin, fragile, resembling a Clementia, 
elongately ovate, moderately tumid; hinge of right valve with 
two bifid diverging cardinal teeth, and one distinct remote 
lateral tooth on either side; pallial sinus slight. Based on J. 
cyrenoides, Desh. (cxv, 33,34); Paris Basin. It recalls Clementia 
in general character, but the dentition of the hinge is distinctly 
that of Cyrenide. 
VE LoRITA, Gray, 1834. 
Disir.—3 sp. Philippines, India, Japan. V. Cyprinoides, 
Gray (cxiv, 39, 40). 
Shell with epidermis, cordiform, triangular, thick, solid ; three 
cardinal teeth, the anterior one of the right valve and posterior 
of the left rather small; lateral teeth large, very finely striated, 
the anterior very large, triangular, the posterior compressed, 
elongated. 
Batissa, Gray, 1847.53/ 
Distr.—30 sp. Polynesia, Australia, E. Indies. B. violacea, 
Lam. (cxiv, 41-48). 
Shell subcordiform, solid, covered with a horny, greenish 
epidermis ; three cardinal teeth in each valve, the right anterior 
and left posterior ones rather small; lateral teeth compressed, 
striated, the anterior very short, posterior elongated. 
CorsrcuLa, Muhlf., 1811. 
Distr.—120 sp. India, East Indies, Philippines, So. America. 
C. cor, Lam. (exiv, 44-46). Fossil. Laramie; N. America. 
Shell subcordiform, solid, close, concentrically striated or 
ridged, covered by a smooth, greenish epidermis; three cardinal 
teeth in each valve, the right anterior and left posterior rather 
small; lateral teeth elongated, compressed, striated; ligament 
prominent, thick; pallial impression with a slight or well-marked 
sinus. 
VELORITINA, Meek. Shell thick, gibbous, obliquely cordate- 
trigonal; beaks elevated, obliquely incurved, and tumid ; poste- 
rior umbonal slopes very prominently rounded ; posterior dorsal 
margins strongly incurved; cardinal teeth typical, excepting 
in being more oblique; lateral teeth with strize very minute or 
obsolete, the posterior one of the left valve often appearing as 
if merely formed by the beveled edge of the incurved dorsal 
margin; ligament small and depressed far below the elevated 
umbonal slopes; surface concentrically striated. Corbicula 
Durkeei, Meek. 
LEPTESTHES, Meek. Shell transversely elongate-subovate, com- 
pressed, typically extremely thin, very oblique ; beaks depressed, 
13 
