Compared to the Sph. s o 1 i d u 1 u m , this species is smaller, more inequi- 

 lateral, less tumid, more compressed, less solid, less heavily sulcated, and its 

 posterior extremity is more distended. 



5. Sph. s t am ineum, Conrad. 



Cyclas staminea, Conrad, Amer. Journ. xxv. 342, pi. 1, f. v. 1834. 



C.fuscata, Rafin., Prime in Bost. Proc. iv. 281, 1852. 



C. bulbosa, Anthony, Prime in loc. sub. cit., iv. 283, 1852. 



Animal, not observed. 



Shell oval, somewhat full, inequilateral ; anterior generally abrupt ; poste- 

 rior slightly distended ; beaks very full and prominent, widely separate at the 

 apex, often eroded ; epidermis dark brownish yellow ; striae heavy ; valves 

 strong ; interior blue ; hinge margin curved ; cardinal teeth double, nearly 

 obsolete ; lateral teeth distinct, strong. 



Long. 9-16 ; lat. 6-16 ; diam. 5-16 inches. 



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

 and Alabama. 



(Cabinet. Academy of Nat. Sci. of Phila., Conrad, Jay and Prime.) 



I have been induced to unite to this species the Cyclas f u s c a t a , Rafin- 

 esque, which I consider as nothing more than a large variety. The Cyclas 

 bulbosa, Anthony, is a little more globose than Mr. Conrad's typical speci- 

 mens, but presents no important characters of difference. The shells of this 

 species found in New Jersey and in Illinois, are larger than those from Ala- 

 bama. 



This species differs from most of our North American ones by its full and 

 very prominent beaks. 



6. Sph. rhomboideum, Say. 



Cyclas rhomboidea, Say, Acad. Nat. Sci. Phil., II. 2, 380, 1822. 



C. cornea, var. 3, Lam., An. s. vert. v. 558, 1818. 



C. elegans, C. B. Adams, Bost. II. 3, 330. pi. 3, f. 11, 1840. 



Animal, syphons reddish yellow. 



Shell subglobular, rhomtic-orbicular, equilateral ; anterior margin trun- 

 cated ; posterior slightly angular ; basal nearly straight ; beaks full, but not 

 prominent ; valves slight, convex towards the beaks, gradually decreasing in 

 fulness towards the margins ; interior blue ; sulcations very delicate ; epider- 

 mis olive green, with often a straw-colored zone on the margins ; young shell 

 more compressed than the adult ; hinge margin nearly straight ; cardinal teeth 

 rudimentary ; lateral teeth distinct, somewhat acute, not elongated. 



Long. 8-16 ; lat. 6-16 ; diam. 5-16 inches. 



Hab. North America, in the States of Vermont, Connecticut, Massachu- 

 setts, New York and Ohio. 



(Cabinet. Academy of Nat. Sci. Phila., Jay, Prime, and others.) 



This, the most attractive species of Sphcerium, is not easily confounded 

 with any other. Up to within a few years it was usually known among col- 

 1 ectors under the name of Cyclas e 1 e g a n s, Adams. I have stated elsewhere* 

 my reasons for considering the Cyclas elegansas identical with Say's shell. 

 Though no longer rare since 1851, when Mr. Whittemore found it in consider- 

 able abundance at one place near Cambridge, Mass., this species does not 

 seem to be very widely distributed ; it is confined to certain special locali- 

 ties. 



7. Sph. d e n t a t u m, Hald. 



Cyclas dentata, Hald., Acad. Nat. Sci. Phila. Proc. i. 100, 1841, 

 Animal, not observed. 



:: Annals of the N.Y. Lyceum, vol. vi. p. 66, 1853. 



