Shell large, ventricose, somewhat equilateral, inferior and anterior margins 

 rounded ; posterior somewhat angular ; beaks large, well rounded, distant, 

 not very prominent ; hinge margin nearly straight ; cardinal teeth single, dis- 

 tinct ; lateral teeth not prominent ; sulcations slight ; epidermis olive green, 

 with a dark narrow zone at some distance above the basal margin. 



Long. 1-2 ; lat. 2-5 ; diam. 3-8 inches. 



Bab. North America, in Oregon. 



(Cabinet. Academy of Nat. Sci. Phila.) 



The young shell is more elongated and more heavily sulcated than the 

 adult ; the beaks are less large and less tumid. This is a well marked species, 

 compared to the Sph. patella, Gould, from the same section of the country 

 it is found to be larger, more ventricose, the beaks are more inflated, and the 

 color of the epidermis is different. 



The only two specimens I have seen of the Sph. dentatum were 

 those from which Mr. Haldeman described the species, an adult and a young 

 one, which he was kind enough to lend me for study ; they are now deposited 

 in the collection of the Academy of Nat. Sci. of Philadelphia. 



8. Sph. fabalis, Prime. 



Cyclasfabalis, Prime, Bost. Proc. iv. 159, 1851. 

 C. castanea, Prime, loc. sub. cit., iv. 160, 1851. 

 C. sulculosa, DeCharpentier, Mss. 1851. 



Animal, syphons crimson. 



Shell transversely oval, compressed, nearly equilateral ; anterior and basal 

 margins rounded ; posterior margin slightly abrupt ; beaks not full, very 

 much depressed ; sulcations moderately heavy, very regular, quite distinct ; 

 epidermis light green, it is, however, sometimes quite dark ; in the young it 

 is often straw color ; valves slight, interior blue ; hinge margin very slightly 

 curved ; cardinal teeth small, assuming the shape of the letter V reversed ; 

 lateral teeth slight ; anterior tooth somewhat more elevated, both placed very 

 nearly on a line with the cardinal teeth. 



Long. 9-16 ; lat. 7-16 ; diam. 4-16 inches. 



Hal). North America, in the States of New York, Ohio, Illinois, Tennessee, 

 Georgia and Virginia. 



(Cabinet. Jay and Prime.) 



This is a very distinct species ; I know of no other to which it bears any 

 resemblance ; it is remarkable for its compressed appearance, and for the de- 

 pression of its beaks. Though pretty widely distributed, it does not seem to 

 be found any where in much abundance. 



The epidermis of the shell is at times so entirely stained with a darkish 

 substance, that it is with difficulty that its color can be detected. 



9. Sph. Occident ale, Prime. 



Cyclas ovalis, (preoc.J Prime, Bost. Proc., iv. 276, 1852. 

 Sph. ovate, Stimps. Adams, rec. gen. 2, 450, 1858. 

 Sph. Occident Jle, Prime, Ac. N. S. Phila., Proc., 295, 1860. 

 Annimal not observed. 



Shell oval, small, pellucid, fragile, equilateral, margins rounded ; valves 

 slight, rather convex ; beaks full, rounded, not much raised; sulcatious very 

 fine, hardly visible ; epidermis horn color ; cardinal teeth very diminutive ; 

 lateral teeth more distinct. 



Long. 5-16 ; lat. 4-16 ; diam. 3-16 inches. 



Hab. N. America, in the States of New York, Vermont, Ohio, Wisconsin, 

 Georgia and in the Hell Gate River, Washington Territory. 

 (Cabinets Academy N. S. of Phila., Jay and Prime) 

 This species is remarkable for its completely oval shape, which renders it 



