4S0 On Gemma, Parastarte, and Psephidia. 



Genus GOMPHINA, Morch. 



Shell trigonal or oval, smooth or concentrically striated. 

 Lunule superficial and circumscribed, but escutcheon not 

 defined. Inner ventral margins smooth or tangentially 

 grooved. Anterior left and posterior right dorsal margins 

 grooved to receive the bevelled and ridged edges of the 

 opposite valve. Hinge-plate short and triangular ; teeth 

 divergent, generally three in each valve, the median of both 

 generally grooved. Pallial sinus small. Pedal scar separate 

 from that of adductor. 



Gomphina, s. s. — Type, Venus dmacina, Ohem. 



Shell trigonal, nearly smooth, and nearly equilateral. 

 Three cardinal teeth in each valve, medians feebly grooved ; 

 the left posterior confluent with the nymph and sometimes 

 rugose, as also is the right nymph. Pallial sinus short and 

 rounded. Valve-margins smooth. 



Subgenus Psephidia, Dall, 1902. 



Type, Psfjyhis lord'', Baird. 



Shell small, subtrigonal and subequilateral, smooth. 

 Hinge with three teeth in each valve, both medians grooved, 

 left posteiior separated from the nymph. Inner margins 

 tangentially grooved and microscopically crenulated. Pallial 

 sinus short, triangular. 



Subgenus Liocyma, Dall, 1887. 



Type, Venus fluctuosa, Gould. 



Shell oval, inequilateral, oblique, concentrically striate. 

 Three teeth in each valve, the medians feebly grooved or 

 entire. Nymphs smooth. Pedal scar not quite separate 

 from adductor. Valve-margins smooth. Pallial sinus short 

 and rounded. 



Subgenus Acoltjs, J-Br., 1913. 



Type, Psephis foveolata, C. & P. 



Shell small, trigonal, equilateral, finely striated. Teeth 

 three in the left valve, the median prominent, triangular, and 

 bifid ; two in the right valve, the anterior absent, the median 

 grooved, and the posterior entire. Dorsal margins irregularly 

 .striated, but ventral margins smooth. Pedal scar separate 

 from the adductor. Pallial line only slightly flexed. 



