52 AMERICAN CORBICULAD^E. 



Long. 0.43 ; Lat. 0.37 ; Diam. 0.18 inches. 



Hab. Nortli America, in Carson and Klamath Rivers, California. (Cabi 

 nets of Gould, Anthony and Prime.) 



Lucina lenticula, GOULD, Bost. Proc. Ill, 1850, 256. 



Cyclas lenticula, GOULD, Atlas Explor. Exped. pi. 36, f. 528. 



This species, of which I obtained specimens from Dr. Gould, is 

 so similar in nearly every respect to S. truncatum, that it is very 

 difficult to tell them apart. The valves of S. lenticula are per 

 haps a little more convex as they approach the region of the beaks, 

 and the hinge-margin a little more curved and less narrow. The 

 young shell is of the same color as the adult, whereas, with S. trun 

 catum, the young is of a lighter color. 



29. Spliirriuiii snt&amp;gt; trans versuni. PRIME. Animal not ob 

 served. 



Shell small, transversely oblong, equilateral, translucent, fragile, com 

 pressed ; beaks central, large, calyculate ; striae very delicate ; epidermis 

 greenish-yellow. 



Long. 0.30 ; Lat. 0.20 ; Diam. 0.10 inches. 



Hab. North America, at Tabasco in Mexico. (Cabinet of Cuming.) 

 Spheerium subtransversum, PRIME, Proc. Zool. XXVIII, 1860, 322. 



The only specimen I have seen of this species was sent to me 

 for description by Mr. Cuming. 



30. Sphaerium argeiitiuum, D ORBIG NY. Animal not ob 

 served. 



Shell oval, small, translucent, compressed ; anterior side short, some 

 what angular, posterior side distended and truncated at the end ; beaks 

 calyculate ; strise delicate ; epidermis greenish-brown ; valves slight, in 

 terior bluish ; cardinal teeth united, lateral teeth hardly visible. 

 Long. 0.31 ; Lat. 0.25 inches. 



Hab. South America, at Montevideo at the base of the Cerro. (Cabinet 

 of the British Museum.) 



Cyclas argentina, D ORBIGNY, Mag. de Zool. 1835. IB. Voy. en Amer. 

 Merid. 1844, 568, pi. 83, f. 5-7. 



It has not been my good fortune to meet with this species. 

 M. D Orbigny says it bears some resemblance to G. calyculata, 

 meaning thereby, I presume, the shell now known to European 

 Conchologists under the name of S, lacustre, Ferussac. 



