88 CANADIAN MICRO-PALiEONTOLOGY. 



lower in front than behind ; ventral curvature of the right valve 

 (woodcut, fig. 6) gentle and nearly uniform ; of the left valve (figs. 

 12, 13, and 14) oblique; the straight hinge-line has two- thirds of the 

 length of the valve; dorsal angles apparent, but not strongly deve- 

 veloped. Surface smooth, with its convexitj^ usually quite in the 

 middle ; eye-spot well marked and simple ; the muscle-spot not visible. 

 These specimens are mostly casts, only fig. 13 retaining some of the 

 test ; and on this there is an accidental mark simulating the muscle- 

 spot. 



In some respects this form approaches Leperdltia Balthica ; but the 

 right valve is too nearly oblong,* and the left valve is too oblique on 

 its lower margin ; nor are the dorsal angles sufficiently pronounced. 



The species is named in honour of J. F. Whiteaves, Esq., F. G. S., 

 Palaeontologist of the Geological Survey of Canada, whose kind 

 courtesy has enabled me to examine this valuable series of Canadian 

 Palaeozoic Ostracoda. 



PI. xii, figs. 11 and 12 are among eight specimens in a hard cream- 

 coloured limestone from Chemahawin, on the Saskatchewan Piver, 

 north west of Cedar Lake, and geologically a little above the beds at 

 Eoche Eouge. Collected by Mr. Tyrrell in 1890. One right valve has 

 its ventral edge slightly swollen after the fashion of the specimen 

 shown in fig. 12 a, pi. xiii. 



PI. xii, fig. 13, is from Old Fort Island, Cedar Lake, in a yellowish 

 crystalline limestone, of the same geological zone as the last mentioned 

 specimen. Collected by Mr. Tyrrell in 1890. 



18. Leperditia c^ca, sp. nov. 



PI. 12, figs. 6, 7, and 9. 



Length, (hinge-line), height. 



Fig. 7 5-7 (3- ) 4- mm. 



Fig. 9 11-? (6-5) 7-5 mm. 



Broadly oblong casts; straight on the back, and gettly curved 

 below ; rounded at the ends, almost semicircular in front, and with a 

 slight slope in the upper part of the hinder curve fig. 7, (x4). Fig 9 

 (x2) makes this postero-dorsal slope too steep, the specimen being 

 damaged there. The ventral margin of the left valve (fig. 7) is turned 



*Fig. 11 makes the outline of the ventral curve much too full by the dotted line ; the wood- 

 cut, fig. 2, gives it exactly, but fails in representing the front extremity, which is much damaged 

 in that specimen. This woodcut has the figure magnified three times to compare with those 

 similarly enlarged on pi. xiii. 



