JONES.] PALiEOZOIC OSTRACODA. 89 



sharply inwards, and bears minute pimples (casts of little pits) along 

 the marginal angle. Surface not very convex, smooth and destitute of 

 any visible ocular and muscular spots. 



These casts are common (fig. 6) in hard, white, thin bedded lime- 

 stone from the foot of the Grand Eapids below Old Portage, near the 

 mouth of the Saskatchewan Eiver. Together with them are many 

 other Leperditice, such as pi. xii, figs. 8 and 15, and pi. xiii, fig. 2, see 

 page 107. Fig. 9 is from a hard, rough, buff-coloured limestone, wea- 

 thering grey, on the Saskatchewan Kiver below (east of) Cedar Lake,^ 

 which is not far north of Lake Winnepegosis. Besides one Isochilina 

 grandis, var. latimargmata, four specimens of this rock contain three Lep- 

 erditice not well exposed. PL xii, fig. 9 is one of them ; and there was a 

 small left valve (not figured) with a sharply inturned ventral margin. 

 Collected by Mr. Tyrrell. I/. Eichwaldi, Schmidt (M6m. Acad. Imp. 

 Sci. St. Petersbourg, Ser. 1, vol. XXI, No. 2, 1873, p. 17; and vol. 

 xxxi, No. 5, 1883, p. 11, pi. i, fig. 1), is one of the few Leperditios that 

 present such a subquadrate outline as the foregoing. 



19. Leperditia Selwynii, sp. nov. 



PI. 12, figs. 1-5. 



Length, (hinge-line), height, thickness of surface. 



Fig. 1 11- (7- ) 7-5 4- mm. 



Fig. 2 12- (9-) 8-5 5* mm. 



t^ig. 3 10- (6-5) 6-5 4- mm. 



JSTeatly Leperditian in shape ; straight on the back, with definite 

 dorsal angles ; curved on the free margins, more fully behind than in 

 front ; surface smooth and of a brownish colour ; traces of a muscle- 

 spot observable in one broken and weathered large specimen. The 

 specimens vary in size according to age; for the left valves, figs. 1 a 

 and 2 a, difl'er in the obliquity of the ventral margin, and the smaller 

 (younger) individual, fig. 3 a, which is the overlapping and therefore 

 the relatively larger valve, is less oblique on the ventral margin than 

 fig. a, and much less oblique than fig. 2 a; probably an older right 

 valve would have a more oblique ventral curvature. 



The subcentral convexity of these valves varies slightly. The ven- 



'••'' The rock outcropping on Cedar Lake was found to be the same as that on the northeast 

 shore of Lake Winnipegosis. It was, however, here found to contain a much larger number of 

 fossils, which clearly determine its age as about that of the Niagara formation of Iowa and 

 Wisconsin. The rock through which the river has cut its gorge at the Grand Rapids also belongs 

 to the same formation." Mr. Tyrrell, in the " Summary Report of the Geol. Surv. Department 

 for 1890," p. 23. 



