SPH^ERIUM. 51 



S. rosaceum, it is less equilateral, more inflated and the margins 

 are less rounded. 



27. Spliaerilim truncatum, LINSLEY. Animal not observed. 

 Shell rhombic-orbicular, lenticular, thin, pellucid, very slightly inflated, 



subequilateral ; anterior side narrower ; anterior margin 

 rounded ; posterior margin nearly a straight line ; basal Fig. 50. 

 somewhat curved ; beaks central, calyculate, approximate 

 at apex ; striae very delicate ; epidermis glossy, light green 

 ish horn color ; valves slight, very little convex ; interior 

 light blue ; hinge-margin very nearly straight ; very narrow ; 

 cardinal teeth diminutive, united at base ; lateral teeth s. truncatum. 

 slight, narrow, not much elongated. 



Long. 0.37 ; Lat. 0.31 ; Diam. 0.15 inches. 



Hob. North America, in the States of Maine, Vermont, Massachusetts, 

 Connecticut, Wisconsin, New York, Ohio, and in Canada. (Cabinets of 

 Linsley, Gould, Prime and Smithsonian Institution.) 



Cyclas calyculata, C. B. ADAMS, Amer. Jour. XI, 1841, 277. 

 Cyclas truncata, LINSLEY, Amer. Jour. VI, 1848, 234, f. 3. 

 Cyclas pellucida, PRIME, Bost. Proc. IV, 1852, 277. 



The specimens from which this description was prepared, the 

 same ones from which Dr. Gould described the original C. trun- 

 cata, are precisely similar to those the late Prof. Adams sent to 

 me labelled C. calyculata, from Vermont, and which I described, 

 in 1852, under the name of C. pellucida. This species is un 

 doubtedly very closely allied to S. lacustre, Fe russac (C. calycu- 

 lala of authors) of Europe, but still the differences are patent 

 enough to authorize its being retained as distinct. Compared 

 with S. partumeium, the S. truncatum is less inflated, transversely 

 less broad, the posterior margin is more abrupt and the hinge 

 slighter. The young, more tumid than the adult, is of a lemon 

 yellow. Found not uncommonly. 



28. Spliaerium lenticula, GOULD. Animal not observed. 

 Shell rhombic-orbicular, lenticular, thin, pellucid, very 



slightly inflated, nearly equilateral ; anterior side nar 

 rower ; anterior margin curved ; posterior margin abrupt, 

 inferior rounded ; beaks central, calyculate, approximate 

 at apex ; striae hardly visible ; epidermis glossy, light 

 greenish horn color ; valves delicate, a little convex 

 towards the region of the umbones ; interior light blue ; 

 hinge-margin nearly straight, narrow ; cardinal teeth hardly visible, united 

 at base ; lateral teeth slight, narrow, not much elongated. 



