36 AMERICAN CORBICULAD^E. 



color is different, and lastly, its hinge-margin is much more 

 curved. 



Compared with S. solidulum, it is more convex, more elon 

 gated, its posterior margin is broader, the hinge-margin is not so 

 much curved, the beaks are fuller, and the sulcations are not quite 

 so heavy ; the color is also different. 



3. Sphaerium sol idiiliim, PRIME. Animal not observed. 

 Shell transversely inequilateral, elongated, slightly convex ; beaks full. 



not very prominent ; anterior margin rounded ; posterior 

 Fig. 27. drawn out to an angle ; base slightly curved ; epidermis 

 variable, dark chestnut or brownish-yellow, with sometimes 

 a yellow zone on the basal margin ; snlcations coarse, irre 

 gular ; interior dark blue ; hinge-margin considerably 

 curved ; cardinal teeth double, in the shape of the letter V 

 reversed ; lateral teeth large ; the anterior placed at an angle 

 with the margin ; the posterior more on a continuation of the curve. 



Long. 0.56; Lat. 0.43; Diam. 0.31 inches. 



Hab. North America, in the States of New York, New Jersey, Ohio, 

 Maryland, Virginia, Indiana and Wisconsin. (Cabinets of the Academy 

 of Natural Sciences of Philadelphia, Smithsonian Institution, Jay and 

 Prime.) 



Cyclas solidula, PRIME, Bost. Proc. IV. 1851, 158. 

 Cyclas distorta, PRIME, loc. sub. cit. IV, 1851, 158. 



This species, which is not uncommon, was probably confounded 

 by our early conchologists with S. sulcatum; it differs from that 

 species, however, in being less elongated, more inequilateral, less 

 convex, the hinge-margin is more curved, and the shell is more 

 solid. 



4. Spliit rium triangulare, SAY. Animal not observed. 



Shell transversely oval, nearly equilateral, 

 Fig. 28. rather full, anterior margin slightly distended, 



rounded, posterior somewhat abrupt, basal round 

 ed ; beaks large, full, prominent ; lines of growth 

 regular, epidermis brownish ; hinge-margin nar 

 row, curved ; cardinal teeth very distinct, assum 

 ing the shape of the letter V reversed ; lateral 

 teeth prominent. 



Long. 0.56 ; Lat. 0.43 ; Diam. 0.25 inches. 

 S. triangulare. 



Eab. North America, in Mexico. (Cabinet of 



the Academy of Natural Sciences of Philadelphia.) 



Cyclas triangularis, SAY, New Harm. Dissem. 1829, 356. 



