JONES.] PALEOZOIC OSTRACODA. 93 



collected by J. B. Tyrrell in 1889 from a small island on the south- 

 east side of Dawson Bay, Lake Winnipegosis. In this limestone, 

 which is made up of organic remains, there are a few minute internal 

 casts of Ostracoda ; but only two are distinct enough for figuring 

 and description. 



One of these small white casts (woodcut, fig. *7) is that of a left 

 valve, leperditioid in shape, suboblong, not so fully rounded in front 

 as behind; hinge line long; front dorsal margin obscured by matrix ; 

 hinder angle sharp, with curve below it. Subconvex, with the greatest 

 fullness rather above the median line and in the posterior moiety of 

 the value. A very faint, circular, subcentral depression is just trace- 

 able. 



This may be a true Isochilina, and I wish to associate with it the 

 name of the taleuted and enthusiastic Geological Surveyor, Dr. G. M. 

 Dawson, after whose father the Bay itself was named. 



5. Elpe Tyrrellii, (sp. nov.). 

 2a 2b 



2 c 

 Fig. 8. Elpe Tyrrellii, sp. nov. a, side view ; h, edge view ; c, end view. 



Magnified 15 diameters. 



Size: Length 1 -13 (hinge-line -66) ; height -16 ; thickness -46 mm. 



This is a white cast of a small carapace, subreniform, obliquely 

 rounded and narrow in front, full with a semicircular curve behind ; 

 ventral margin boldly curved ; dorsal margin somewhat depressed and 

 hollow in the middle. Surface convex, and most so below the median 

 line and in the posterior moiety. 



This is much like Meek's Cythere Cincinnatiensis (Proceed. Acad. 

 Nat. Sci., 1872, p. 331, and Geo. Surv. Ohio, Paleont., vol. I, 1873, 

 p. 158, pi. xiv, figs. 1 a-d ) ; but is contracted at the anterior moiety. 

 The Ohio form is variable and may be represented by more than one 

 species (Meek). It is, however, much more like some drawings of 

 the same species, kindly sent to me in 1888 by Mr. E. O. Ulrich of 

 Newport, Ky. The proportions are only slightly different, a^Cincin- 

 nati specimen having— Length 1- (hinge-line '72); height 'QQ] 



