MOLLTJSCA OP LOWER CANADA. Ill 



beaks large, calyculate, slightly inclined towards the anterior, very 

 approximate at apex : valves slight, very convex, especially in the- 

 region of the umbones; striae delicate, regular, hardly perceptible ; 

 epidermis glossy in some cases, very variable in colour, but gener- 

 ally of a greenish-horn tint ; at times of a brilliant yellow or straw 

 colour (in Canadian specimens often translucent glossy white) : 

 hinge-margin curved, narrow ; cardinal teeth very small, united 

 at base ; lateral teeth slight elongated ; very narrow. 



Long. 6-16; lat. 5-16;diam. 4-16. inches. 



Unlike any other Canadian species. 



The descriptions of the Lower Canadian species of Sphoerium 

 have been taken from Mr. Prime's able monograph. The ensuing 

 descriptions are original, except in the case of Limnsea ampla, 



Figure 8. 

 Pisidium Virginicum, Brongniart. 



Shell ovate, elliptical, oblique; strongly concentrically sulcate; 

 " beaks placed much nearer one end;" slightly elevated, rounded,, 

 with a decided inclination to the anterior portion of the shell 

 Posterior end elongated, rounded ; anterior portion truncate ; 

 ventral margin convex. Easily distinguished from all the Lower 

 Canadian Pisidia by its large size, strong concentric snlcations, 

 and general outline. 



Figure 9. 



Pisidium altile, Anthony. 



Shell sub-triangular, very tumid (except in the variety compres- 

 sum, which may prove a distinct species), especially in the region 



