48 AMERICAN CORBICULAD^. 



22. Sphaerium transTersum, SAY. Animal white, syphonal 

 tubes pink, foot white. 



Shell transversely oblong, elongated, subinequilateral, translucent ; an 

 terior side narrow ; anterior margin 



Fig. 45. . rounded, posterior margin subtrun- 



cate, basal very much curved ; beaks 

 placed somewhat on the anterior side, 

 large, calyculate, very much raised 

 above the outline of the shell ; striae 

 very delicate ; epidermis greenish- 

 yellow, of a darker shade at times 

 on the region of beaks ; valves slight, 

 interior bluish ; hinge-margin very 

 nearly straight, narrow ; cardinal teeth 

 S. transversum. compressed, in the shape of the letter 



V reversed, and very much expanded ; 

 lateral teeth slightly elongated. 



Long. 0.62; Lat. 0.43; Diam. 0.25 inches. 



Bab. North America, in the States of New York, Pennsylvania, Ohio, 

 Kentucky, Arkansas, Alabama, and in Canada. (Cabinets of Jay, Prime 

 and the Smithsonian Institution.) 



Cyclas transversa, SAY, New Harm. Dissem. II, 1829, 356. 

 Cyclas detruncata, PRIME, Bost. Proc. IV, 1851, 155. 

 Cyclas gracile, PRIME, loc. sub. cit. IV, 1851, 156. 

 Cyclas constricta, ANTHONY, loc. sub. cit. IV, 1852, 274. 



This large and delicate species is remarkable for its very trans 

 verse shape and for the narrowness of the anterior extremity as 

 compared to the posterior. The form of the shell recalls that of 

 many of the small species from the West Indies and South 

 America. It is found in considerable abundance. 



C. detruncata does not differ sufficiently from the type to con 

 stitute even a variety. C. gracilis is a large variety of S. trans 

 versum ; it is a little more inflated and of a darker color. C. 

 constricta is nothing more than a difformed specimen of Say s 

 species, having a perpendicular furrow up the centre of each 

 valve, caused by some accident occurring to the shell during its 

 growth. 



23. Spliivriiim contractum, PRIME. Shell transversely ob 

 long, inequilateral, translucent, moderately full ; anterior side narrow : 

 anterior margin rounded; posterior margin subti uncate ; basal rounded ; 

 beaks inclined towards the anterior, calyculate, raised above the outline 



