44 AMERICAN CORBICULAD^E. 



Long. 0.50; Lat. 0.51 indies. 



Hab. North America, at Sumass Prairie, Frazer River, British Columbia. 

 (Cabinet of the British Museum.) 



Sphserium tumidum, W. BAIRD, Proc. Zool. 1863, 69. 



&quot; This shell is of a tumid, swollen figure, and of an ovate- 

 trigonal shape. The color externally is dark olive, and it is 

 strongly ribbed concentrically. The beaks are prominent, and 

 frequently eroded. The inner surface is of a bluish tint. The 

 ventral or lower margin is rounded.&quot; 



11. Spliaerium spokaiii, W. BAIRD. S. testa rotundato-ovata, 

 cornea, concentrice transversim conferte minute striata, nitida, sub lente 

 obsolete punctata ; umbonibus rotundatis, obtusis ; interne albida ; mar- 

 gine ventrali rotundato. 



Long. 0.48 ; Lat. 0.51 inches. 



Hab. North America, in the Spokane and Kootanie Rivers, British Co 

 lumbia. (Cabinet of the British Museum.) 



Sphasrium spokani, W. BAIRD, Proc. Zoo*!. 1863, 69. 



This shell is smaller than S. tumidum, more rounded, and with 

 more obtuse beaks. The striae or riblets are much less distinct ; 

 the color is pale horny externally, and white internally. It has a 

 shining appearance ; but when examined by the lens, the surface 

 is seen to be indistinctly punctate. The specimens taken from 

 the Spokane River are much larger than those collected in the 

 Kootaine. 



6. BEAKS TUBERCULAR OR CALYCULATE. 



18. Spliaerium elevatum, HALDEMAN. Animal not observed. 

 Shell ovate, orbicular, nearly spherical, cavity- 

 Fig. 40. large, equilateral, margins well rounded ; beaks 

 central, slightly inclined towards the anterior, 

 lapping over the outline of the shell, large, tumid, 

 approximate, calyculate, prominent; hinge-mar 

 gin slightly curved ; cardinal teeth united, promi 

 nent ; lateral ones elongated, large ; valves very 

 strong, interior bluish ; surface smooth, striation 

 light, irregular ; color brownish-olive, greatly 

 varied by zones of a lighter shade, a zone of 

 S. elevatum. bright yellow bordering the inferior and part of 



the lateral margins. 

 Long. 0.56 ; Lat. 0.50 ; Diam. 0.31 inches. 



