180 VENERID^. 



Subfamily DOSINIIN^. 



Shell orbicular, mostly flattened and concentrically striate ; 

 pallial sinus oblique, triangular. Siphons united; foot subquad- 

 rangular, without byssiferous furrow. 



DosiNiA, Scopoli, lltT. 



Sfyn.— Artemis, Poll, 1*791. Orbiculus, Muhlf., 1811. Exoleta, 

 Brown. Asa, Leach. 



Dintr. — 100 sp. Boreal — Tropical seas; low-water — 80 

 fathoms. Fossil, 13 sp. Cret. — ; IJnited States, Europe, South 

 India. D. discus, Eeeve (cxiv, 32). 



Shell orbicular, compressed, concentrically striated, pale, 

 ligament sunk ; lunule deep ; hinge like Cytherea ; margins 

 even ; pallial sinus deep, angular, ascending. 



Animal with a large hatchet-shaped foot, projecting from the 

 ventral margin of the shell ; mantle-margins slightly plaited ; 

 siphons united to their ends; orifices simple, palpi narrow. 



Gemma, Deshaj^es. 



Syn. — Tottenia, Perkins, 1869. 



Distr. — U. S. G. gemma, Totten (cxiii, 29). 



Shell rounded, subtriangular, subequilateral, smooth, margins 

 crenulated within ; hinge short and narrow ; three teeth in the 

 left valve, the middle one conical, arcuated ; two divergent 

 teeth and an intermediate pit in the right valve ; pallial impres- 

 sion marginal, with a narrow deep sinus. 



The species of this genus are very small, not exceeding 8'5 

 mill, in diameter. 



Cyprimeria, Conrad, 1864. 



Distr. — Cretaceous ; North America, Europe. G. discus, 

 Matheron (cxv, 39, 40, 42). 



Shell lentiform ; hinge of right valve broad, with a bifid 

 oblique cardinal tooth and two oblique acute anterior teeth, 

 with an intermediate pit for the reception of the tooth in the 

 opposite valve. 



Cyclina, Deshaj^es. 



Distr. — 10 sp. Senegal, India, China, Japan, West America. 

 Fossil, 1 sp. Miocene ; Bordeaux. C. Chinensis, Chemn. 

 (cxiv, 33). 



Shell orbicular, somewhat convex, close ; margins usually 

 finely crenulated ; beaks inclined anteriorly, no lunule; three 

 small cardinal teeth, narrow, divergent and unequal ; no lateral 

 teeth ; two large muscular impressions, anterior oval, posterior 

 semilunar; pallial impression short, the sinus deep and angular; 

 ligament long and narrow. 



