178 VENERlDiE. 



teeth, the anterior as thick as the middle one, or thicker, and a 

 straight, compressed, transversely rugose lateral tooth parallel 

 with the margin above it ; pallial sinus deep, and similar to that 

 in Carj^atis, Romer. G. Tippana^ Conr. Cretaceous ; U. S. 

 Too closely allied to the next group. 



CARYATis, R'imer, 1862. (Olim Pitar, Rom., 1857.) Shell 

 cordate or subtrigonally ovate, usually of moderate thickness 

 and somewhat inflated, white or j^ellowish brown colored, con- 

 centrically finely striated, pallial sinus alwa3^s distinct, trian- 

 gular or obtuse. Venus tumenSj Gmelin, is the type of this yery 

 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 (cxiv, 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; 

 cartilage-plate granulated ; pallial sinus deep and angular. 3 

 sp. Eocene ; United States. C. leyiticidaris, Rogers (cxv, 38). 



DiONE, Cray, 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. Romer notices 13 sp. 

 G. lupanaria, Desh. (cxiii, 23). 



AMiANTis, Carp., 1865. Type, Gytherea callosa, Con. This 

 group certainly does not deserve to bear a special name. It 

 only differs by having the fulcra thicker than most other species, 

 and rugose. The general form and dentition of the hinge are 

 extremely like Gylh. ( Gallista) erycina, Linn. 



MACROCALLiSTA, Meek. Shell transversely elongate-oval, with 

 surface smooth ; pallial sinus and hinge nearly tjqDical, 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 giganteo,, Gmelin. 



ARTENiA, 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. Gytherea 

 staminea, Con. (cxiv, 31). Tert. ; U. S. This appears to be very 

 close to some species of Dione. 



