CORBICULA. 3 



Tliis g:enus has of late years been very generally adopted Ijy 

 European conchologists. We do not find any living representa- 

 tive of this genus on the northern portion of this continent, the 

 most northern extremity to which it extends being Mazatlan. As 

 yet we know of no species from the West Indies, either living or 

 fossil ; in South America, on the contrary, they seem to exist in 

 considerable abundance. 



A peculiarity of the Corhicvla found in America, which they 

 share with our Gyrena, lies in the fact that the palleal impression 

 always terminates in a sinus, whereas in the species from other 

 regions it is simple. 



1. Corl>i('Ula coiiTexa, Deshayes. — Shell orbicular, lieart-sliaped, 

 inequilateral, solid ; the anterior side the shorter ; beaks 



tumid, rounded, opposite ; lunula indistinct, ligament 

 short, prominent; valves convex, the interior wliite ; 

 epidermis light-green; striae irregular , delicate ; three 

 unequal cardinal teeth, the central bifid ; lateral teeth 

 nearly equal, narrow, delicately striated, palleal impres- 

 sion terminating in a small trigonal sinus. 



Long. .72; Lat. .6(5; Diam. .50 inch. 



" 18; '• !<-!; " 13 mill. C. com-exa. 



^ Hah. North America, at Mazatlan, in Mexico. 

 (Cabinets of Cuming and Prime.) 



Corbicnla conrexa, Deshayes, Proc. Zool. Soc. XXII, 1854, 342. 

 Corbiciila ventricosa, Prime in litt. 



I have never seen the original C. convexa, but have very little 

 doubt from the description Mr. Deshayes gives of that species, 

 that the shell in my cabinet, which I called C. ventricosa, is 

 identical with it. 



This species is easily distinguished by its globular shape, which 

 renders it very different from all others ; externally it is somewhat 

 similar to the young of Cyrena mexicana. 



2. CorlfiCMla paraiieiisis, Deshayes. — Shell small, rounded-oval, 

 somewhat iuti.ited, inequilateral ; anterior side short, rounded, 

 posterior side somewhat abrupt ; beaks small, inclined towards 

 the anterior; valves full, strong, interior white; striae very 

 light, hardly visible ; epidermis light-green ; hinge-margin 

 rounded, thick; three cardinal teeth, unequal, divergent; 

 lateral teeth nearly equal, the anterior one a little arched, 

 finely striated ; palleal impression terminating in a small sinus. 



Fig. 2. 



