354 PROCEEDINGS OF THE NATIONAL MUSEUM. 



but the escutcheon not defined; inner margins smooth, pallial sinus 

 ample, elongate, somewhat ascending, pointed in front; middle car- 

 dinal stout, the others slender; the posterior cardinals feebly grooved, 

 the others entire; the cardinals of the right valve discontinuous where 

 they touch the dorsal margin and not sei)arated from the latter by a 

 groove; anterior lateral adjacent, distinct; nymphs and teeth smooth; 

 dorsal margins grooved as in Meretrix. Widely distributed in the 



Tropics. 



Romer's original name, Pifa/\ is a vernacular African word, not 

 really entitled to be used without Latinization, for which, in 1862, he 

 substituted Oaryatis, which is preoccupied in Lepidoptera since 1816. 

 It is probable that a Latinized form as above should be adopted for 

 the group. 



Section Pltaria s. s. Type, Vemis tumens Gmelin. 



Shell smooth or with concentric striation, usually convex, subtrig- 

 onal or ovate, with a pointed sinus. 



Section Ilyphantosoma Dall, 1902. Type, Cytherea carbasea Guppy, 

 1866. Oligocene. 



Shell with zigzag sculpture on the surface like Textivenus Cossmann, 

 of the Venerine series. 



Section Ticelhia Cossmann, 1886. Type, Cytherea teUinarai 

 Lamarck. Eocene. 



Shell pointed l)ehind with a Tellina-like twist to the valves, which are 

 concentrically striate; hinge as in Pltdrla; pallial sinus short, bluntly 

 rounded. 



Subgenus Hysteroconcha Fischer, 1887. Type, Verms dione Linnaeus. 



Shell subtrigonal, plump, concentrically laminate; lunule and escutch- 

 eon defined by incised lines and impressed, the laminae becoming spinose 

 near the boundary of the escutcheon; shell with tinted coloration not 

 in patterns; inner margins smooth, pallial sinus linguiform, ample, free, 

 slightly ascending; hinge as in Pitaria, the edges of the nymphs finely 

 granular and the stout middle cardinal sometimes obscurel}^ channeled. 



Tropical American waters. 



This is Dione Gray, 1817, not Gray, 1851, nor Hiibner, 1816; and 

 Venus Megerle, 1811, not of Lamarck, 1799. 



Section Lamelliconclta Dall, 1902. T^^pe, Cytherea condnna Sowerby . 



Shell trigonal, subcompressed, concentrically ribbed or laminate, 

 without spines; the edges of the njaiiphs smooth; otherwise like 

 Hysteroconcha. 



Tropical seas, especially in America. 



Genus CYTHEREA Bolten, 1798. 



Types (by elimination), Venus puerpera Linngeus, V. rugosa Gmelin, 

 and V. verrucosa Linnteus. 



Shell large and rotund, convex, with strong predominantly concentric 

 sculpture with well-marked lunule and escutcheon, the latter unequally 



