58 CANADIAN PERIOD. 



G. metelliis Billings, fi-om the Quebec strata of Canada. The curvature and 

 propoi-tions are similar to those of that species, and the septa are equally 

 numerous and close-set. 



ARTICULATA. 



Class CRUSTACEA. 



Order OSTRACADA. 

 Family CYPRIDINID^. 



Genus LEPERDITIA Rouault, 1851. 



Leperditia bivia White. 



Plate III, fig. 7, a, h, c, and d. 



leperditia bivia White, 1871, Expl. & Surv. west 100th Merid., Prelim. Rep. luvert. 

 Foss., 11. 



Shell not quite equivalve, inflated, the gi'eatest transverse diameter 

 being about midlength and below the middle ; obliquely subovate in out- 

 line, widest behind the middle ; the straight hinge-hne about equal in 

 length to two-thirds the entu-e length of the shell, and ending both poste- 

 riorly and anteriorly in a small, distinctly projecting angle, which it forms 

 with the anterior and posterior margins respectively; posterior margin 

 obliquely rounded, and provided with a moderately broad, somewhat flat- 

 tened border; anterior margin abruptly rounded, having also a similarly- 

 flattened border ; the flattening of the borders of both valves and at both 

 ends becoming obsolete upon reaching the ventral margin, which is broadly 

 rounded ; ventral border of the left valve bent shai-j^ly inward, and even a 

 little upward, producing a naiTow, plain, area-hke sui-face there, which 

 tapers to a sharp point at each end, and is nearly equal in length to the 

 hinge-line ; ventral border of the right valve not bent inward like that of 

 the left, but the general convexity of the valve extends to the ventral edge. 

 Upon the ventral border of this valve, near its edge, there are two distinct, 

 comjDaratively large pores, which open divergingly upon the surface ; the 



