408 PROCEEDINGS OF THE ACADEMY OP 



Shell rhombic-ovate, inequilateral, moderately compressed ; anterior mar- 

 gin truncated, posterior more distended, basal curved ; beaks rounded, in- 

 clined towards the front, slightly tumid, separate at apex ; sulcations coarse ; 

 epidermis delicate, light brown ; valves strong, interior white ; hinge margin 

 nearly straight, moderately broad ; cardinal teeth single, distinct ; lateral 

 teeth moderately developed. 



Long. 8-16 ; lat. 6-16 ; diam. 4-16 inches. 



Hab. N. America, at San Pedro in the State of California. 



(Cabinet. Gould and Prime.) 



Compared to the Sph. sulcatum it is slighter, less sulcated, more com- 

 pressed and less tumid. This species is rare, the only specimens I have seen 

 were kindly presented to me by Dr. Gould. 



11. Sph. patella, Gould. 



Cyclas patella, Gould, Bost. Proc, iii. 292, 1850. Atlas U. S. Explor. 

 Expedit., pi. 36. 



Animal not observed. 



Shell rounded oval, lenticular, compressed, equilateral ; margins generally 

 rounded ; beaks central, small, hardly raised ; valves slight, interior white ; 

 sulcations extremely fine ; epidermis light, of a yellowish brown color; car- 

 dinal teeth very diminutive, so placed as to assume the shape of the letter V 

 reversed ; lateral teeth not prominent, elongated. 



Long. 7-16 ; lat. 5-16 ; diam. 3-16 inches. 



Hab. N. America, in Oregon. 



(Cabinet. Gould and Prime.) 



This species is peculiar, owing to its compressed oval shape and rounded 

 beaks ; compared to the Sph. f 1 a v u m it is more oval, more equilateral, and 

 its beaks are less tumid. The specimens in my cabinet came from Dr. Gould. 



12. Sph. Vermontanum, Prime. 



Proc. Ac. N. S. Phil. 128, 1861. 



Animal not observed. 



Shell very oblique, tumid, inequilateral, full ; anterior margin abrupt, pos- 

 terior drawn out to an angle, basal slightly curved ; beaks large, full, promi- 

 nent, placed very much towards the anterior, in which direction they are 

 slightly inclined ; sulcations coarse, moderately regular ; epidermis light 

 green ; ligament conspicuous ; valves solid, interior light blue ; hinge margin 

 much curved, broad ; cardinal teeth strong, representing the letter V reversed ; 

 lateral teeth elongated, strong. 



Long. 9-16 ; lat. 6-16 ; diam. 4-16 inches. 



Hab. N. America, in Lakes Champlain and Memphramagog, Vermont. 



(Cabinet. Prime.) 



Remarkable for its very oblique and tumid shape, and for the abruptness of 

 its anterior margin. Compared to the Sph. st a m i n e u m, it is more tumid 

 and less heavily sulcated ; it is lsss elongated and more tumid than the Sph. 

 striatinum. Quite rare. I have never seen but a few specimens of this 

 species, which were received from the late Prof. Adams, of Amherst. 



13. Sph. emarginatum, Prime. 



Cijclas emarginata, Prime, Bost. Proc. iv. 156, 1851. 



Animal not observed. 



Shell triangular, nearly equilateral, convex, tumid, anterior and posterior 

 margins abrupt, posterior slightly more distended, basal margin curved ; valves 

 solid, interior white ; beaks very full, prominent, nearly central ; ligament 

 distinct ; sulcations regular, not heavy ; epidermis brown, with several nar- 

 row transverse zones of a dark color at regular intervals ; hinge margin 



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ec. 



