86 PKOCKKDINGS OF J'HK MALACOLOGICAL SOCIETY. 



three divergent teeth in each valve, the right posterior being 

 generally bitid or composed of two larainse ; the left posterior is 

 a sliort tooth crossing the hinge-plate. Pallial sinus variable. 



dementia, s.s. Type, Venus papyracea, Graj', 



Shell thin, oval, concentrically undulated and striated. Hinge 

 weak, teeth separate, riglit posterior bifid or composed of two 

 compressed plates, median and anterior near together, left median 

 sometimes bifid. Pallial sinus generally subangular and ascending. 

 Pedal scar large, oval, and opening narrowly into that of the adductor. 



7Wyh<(V?, Jukes-Browne, 1914. Type, dementia ffranifera, ^ow. 



Shell thin, oblong, very inequilateral, ornamented with irregular 

 divaricate or reticulate strife. No escutcheon. Hinge narrow, teeth 

 sliort, and anterior concavity small ; all the teeth entire, the right 

 posterior being tall and narrow, the left very slight and feeble. 

 Pallial sinus very large and deep, and partly confluent with the 

 })allial line. Pedal scar large and confluent with that of adductor. 



Sub-ffenera. 



Flaventia, Jukes- Browne, 1908. Type, Venus ovalis, Sow. 

 (a Cretaceous fossil). 



Shell elongate-oval, fairly strong, with a defined Innule. Teeth 

 all entire, except tlie right posterior, which is widely bifid, the 

 hinder lamina being much longer than the other; left median narrow 

 and oblique, anterior triangular. Pallial sinus deep, ascending and 

 rounded. 



Psathura, Deshayes. Type, Venus fragilis, Lam. (an Eocene fossil). 



Shell thin. Teeth small; right posterior bifid, median grooved; 

 all in left valve entire. Pallial line without inflection. 



Genus CrCLiNA, Deshayes, 1849. 



Type, Venus sinensis, Gmelin. 



Shell orbicular, convex, concentrically striated with subordinate 

 radial striae in the typical section. No defined lunule or escutcheon. 

 Hinge-plate Avell developed, with a sliort anterior and long posterior 

 extension, so that the teeth only occupy a small space. Both posterior 

 teeth are short, and traverse the plate obliquely. Right posterior and 

 sometimes left median bifid. Pallial sinus deep and ascending. Pedal 

 scar small and confluent with that of adductor. 



Cyclina, s.s. Valve-margins crenulated. Pallial sinus angular in 

 sitiensis, but rounded in Jlavida, and subangular in orientalis. 



Sub-ffenus. 



Cyelinella, Dall, 1902. Type, Dosinia tenuis, Recluz. 

 Hinge-plate and teeth like that of Cijclina, but valve-margins smooth. 

 Pallial sinus sharply angular, ascending. 



Genus Gemma, Deshayes, 1853. 

 As I have recently described this genus in the Annals and Magazine 

 of Natural History ^ and have given a corrected description of it with 



1 Ser. VIII, vol. xii, p. 473, 1913. 



