348 PROCEEDINGS OF THE NATIONAL MUSEUM. 



C. Lateral teeth absent, no lunule or escutcheon. 



Genus CYCLINA Deshayes. 1849. 



Type, Yenns sinensis Gmelin. China seas. 



Soft parts like Dosinia; shell orbicular, concentrically and radially 

 striate, without lunule or escutcheon; inner margins crenate; pallial 

 sinus angular, ascending; teeth as in Dosinia, but without laterals, the 

 posterior right cardinal obsolete. 



It is not Oyclinus Kirby, Goleoptera, 1837. 



Genus CLEMENTIA Gray, 1842. 



Type, Venus papyracea i}mj . 



Soft parts as in Dosinia, according to Woodward; valves thin, con- 

 centrically unduhite, convex, without lunule or escutcheon; inner 

 margins simple, sharp; pallial sinus subangular, ascending; three car- 

 dinal teeth in each valve, the posterior right cardinal bifid; lateral 

 teeth absent. 



This is Blainvillia Huppe, 1854, not of Desvoidy, Diptera, 1830. 



Subfamily MIERJETRICHST.^:. 



An anterior lateral tooth present; though sometimes obsolete, traces 

 of it can always be detected in normal specimens. 



Genus GRATELOUPIA Desmoulins, 1828. 



Type, Donax irregularis Basterot. Miocene. 



Valves elongate-oval, concentrically striate; three cardinals in each 

 valve, the posterior right cardinal fused with the nymphal rugosities; 

 the pallial sinus long and acute, reaching to the vertical of the anterior 

 lateral lamina. 



Subgenus Cytheriopsis Conrad, 1865. Type, Cyth&rea hydana Con- 

 rad. Eocene. 



Valves trigonal, recalling Tivela, the left posterior cardinal fused 

 with the nymphal rugosities; the pallial sinus short and rounded. 



This is not Cytlieropsis McCoy, 1849, and if the two names are 

 judged incompatible, might be called Grateloupina. It is probably 

 the precursor of Grateloupia and Tivela. 



Genus TRANSENNELLA Dall, 1883. 



Type, T. conradina Dall. 



Shell small, having the general form and coloration of Tivela, but a 

 hinge with three cardinals in each valve, the middle left cardinal bifid, 

 and an elongate left lateral received into a socket in the opposite valve; 

 the hinge has no rugosities, the lunule but not the escutcheon is defined, 

 internal margins sharply tangentially grooved with numerous sulci; 

 the pallial sinus angular, free, obliquely ascending. 



