44 AMERICAN CORBICULAD^. 



Long. 0.50; Lat. 0.51 inclies. 

 Iluh. Nortli America, at Sumass Prairie, Frazer River, British Columbia. 

 (Cabinet of the British Museum.) 



Sphserium tumidum, W. Baikd, Free. Zool. 1S63, G9. 



" 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." 



IT. Spliaeriuiu spoliani, 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.) 



Spkieriiim sjiokani, W. Baird, Proc. Zool. 1803, 69. 



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

 more obtuse beaks. The stria 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. 



h. Beaks tubercular or caltculate. 



IS. Spliaeriuni elevatum, Haldemax. — 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- 

 jin slightly curved ; cardinal teeth united, promi- 

 nent ; lateral ones elongated, large ; valves very 

 strong, interior bluish ; surface smooth, striation 

 light, iriegular ; color brownish-olive, greatly 

 varied by zones of a lighter shade, a zone of 

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



the lateral margins. 

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



