178 ] VENERID A. 
teeth, the anterior as thick as the middle one, or thicker, and a 
stra ight, compressed, transversely rugose lateral tooth parallel 
with ‘the margin above it; ; pallial sinus deep, and similar to that 
in Caryatis, ‘Rimer. OC. Tippana, Conr. Cretaceous; U. 8S. 
Too closely allied to the next group. 
CARYATIS, Rimer, 1862. (Olim Pitar, Rom., 1857.) Shell 
cordate or subtrigonally ovate, usually of moderate thickness 
and somewhat inflated, white or yellowish brown colored, con- 
centrically finely striated, pallial sinus always distinct, trian- 
cular or obtuse. Venus tumens, Gmelin, is the type of this very 
well-marked form of Cytherea; its distinction from others is of 
great importance in fossil conchology, for to it mostly appear to 
belong the oldest representants of the genus; of recent species, 
Romer describes sixty, and adds two doubtful ones. C. Alcyone, 
Romer (exiv, 36, 37). 
DOSINIOPSIS, Conrad, 1864. Shell exteriorly like Dosinia. 
Cardinal teeth three in each valve; posterior tooth of right 
valve bifid; in the left valve, a thick rugose lateral tooth fitting 
into a cavity in the opposite valve ; under the umbo is a pit; 
eartilage-plate granulated; pallial sinus deep and angular. 3 
sp. Eocene; United States. (. lenticularis, Rogers (cxv, 38). 
DIONE, Gray, 1847. Shell moderately compressed, always 
concentrically densely sulcated, and with a more or less dis- 
tinct ridge running from the beaks in an easy curve to the 
infero- -posterior margin; this ridge is sometimes provided with 
spines; pallial sinus moderate, always distinct, usually lingui- 
form. The type is Venus dione, Linn. Rémer notices 13 sp. 
C. lupanaria, Desh. (exili, 23). 
AMIANTIS, Carp., 1865. Type, Cytherea callosa, Con. This 
group certainly does not deserve to bear a special name. It 
only differs by having the fulera thicker than most other species, 
and rugose. The general form and dentition of the hinge are 
extremely like Cyth. ( Callista) erycina, Linn. 
“MACROCALLISTA, Meek. Shell transversely elongate-oval, with 
surface smooth; pallial sinus and hinge nearly typical, excepting 
that the sublunular or anterior lateral tooth is generally more 
compressed, more oblique, and more remote from the cardinal, 
and the posterior lateral much more elongated, and nearly 
horizontal. Venus gigantea, Gmelin. 
ARTENTA, Conrad, 1870. Shell triangular, thick; surface with 
acute, concentric, prominent ribs; hinge with three cardinal 
teeth in the right valve, two of them diverging, distant, the 
anterior one under the apex robust, direct, curved ; left valve 
with three diverging distant teeth; lateral tooth very small, 
pyramidal; pallial sinus very small and angular. Cytherea 
staminea, Con. (exiv, 31). Tert.; U.S. This appears to be very 
close to some species of Dione. - 
