18 



Long. 6-16; lat. 5-16; diam. 5-32 inches. 



Hab. N. America, in the States of Maine, Vermont, Massachusetts, Con- 

 necticut, New York and Ohio. (Cabinets Linsley, Gould and Prime.) 



The specimens from which this description was prepared, the same ones 

 from which Dr. Gould described the original Cyclas t r u n c a t a, are pre- 

 cisely similar to those the late Prof. Adams sent to me labelled Cyclas c a 1 y- 

 c ulat a, from Vermont, and which I described, in 1852, under the name of 

 Cyclas pellucid a. This specicies is undoubtedly very closely allied to 

 the Sph. lacustre, Ferussac (Cyclas calyculataof authors) of Europe, 

 but still the differences are patent enough to authorize its being retained as 

 distinct. Compared to the Sph. p a r t u m i u m, the Sph. 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. 



34. Sph. lenticula, Gould. 



Lucina lenticula, Gould, Bost. Proc., iii. 256, 1850. 



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



Animal not observed. Shell rhombic-orbicular, lenticular, thin, pellucid, 

 very slightly inflated, nearly equilateral ; anterior side narrower ; anterior 

 margin curved ; posterior margin abrupt, inferior rounded ; beaks central, 

 calyculate, approximate at apex; strise 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. 



Long. 7-16 ; lat. 6-16 ; diam. 3-16 inches. 



(Cabinets Gould, Anthony and Prime.) 



Hab. N. America, in Carson River, California. 



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

 in nearly every respect to the Sph. truncatum, that it is very difficult to tell 

 them apart. The valves of the Sph. lenticula are perhaps a little more 

 convex as they approach the region of the beaks, and the binge margin a 

 little more curved and less narrow. The young shell is of the same color as 

 t the adult, whereas, with Sph. truncatum, the young is of a lighter color. 



Fossil Species. 



35. Sph. recticardinale, Meek and Hayden, Ac. N. S. Phil., Proc., 176, 



1860. 



Shell of medium size, transversely subelliptical, rather compressed, very 

 thin ; anterior side rounded ; base forming a regular semielliptic curve ; pos- 

 terior extremity obliquely subtruncate above and rather narrowly rounded 

 below ; cardinal margin long and straight ; beaks very small, compressed and 

 projecting but slightly above the hinge, located nearly half way between the 

 middle and the anterior end ; surface marked by moderately distinct, irregular 

 lines of growth. 



Long. 0-55 ; lat. 0-36 j diam. 0-24 inch. 



Hab. Near the mouth of Grand River, on the Upper Missouri, Nebraska, 

 U. S. of America. Tertiary Formation. 



36. Sph. pi an urn, Meek and Hayden, Ac. N. S. Phil., Proc., 175, 1860. 



>11 rather small, broad oval or subcircular, much compressed ; extremi- 

 ties more or less regularly rounded, the posterior margin being sometimes 

 tamtly subtruncate ; base semioval in outline ; cardinal margin rounding 

 gradually from near the middle ; beaks very small, compressed, and scarcely 

 extending beyond the hinge margin, nearly central ; surface marked by fine, 

 irregular, obscure concentric strise. 



