80 WHITBAVES ON FOSSILS FEOM THE 



Approximate dimeusious of the most perfect specimen collected : — actual length along 

 the median line of the most convex side, lt9 millimetres, or about seven inches and a 

 half (but as a considerable piece is broken off the posterior end, its entire length when 

 perfect was probably an inch longer than this) ; maximum dorso-veutral diameter of the 

 same, 106 mm. ; greatest lateral diameter, 55 mm. 



The beautiful specimen figured, which is a well preserved cast of the interior of the 

 shell, collected by Mr. IT. Chesterton at East Selkirk, was recently presented to the Museum 

 of the Survey by the President (Mr. Charles N. Bell) and members of the Manitoba 

 Historical and Scientific Society. A similar but less perfect specimen was obtained at the 

 same locality in 1884 by Mr. T. C. Weston. 



Oncoceeas gibbosiim. (N. Sp.) 

 (Plate XV, figs. 2 and 3.) 



Shell resembling that of the preceding species in external form and apparently also 

 in the characters of its interior, but differing therefrom only in its much smaller size. 

 Thus, the smallest specimen of O. magnum known to the writer must have been a little 

 more than eight inches in length, when perfect, and the largest fully eleven, whereas in 

 the present species, out of fourteen specimens collected, the smallest could not have been 

 more than three inches and a half long when perfect, and the largest four and a half. 

 These two series of specimens, too, do not seem to be connected by any intermediate 

 gradations in size. 



In one of the specimens of O. gibbosiom from Swampy Island, the surface of the test 

 of the septate portion is faintly costulate transversely, as represented on fig. 3. 



Big Island, Washow Bay, Bull Head Ba}-, and Jack Fish Bay or Pike Head, Lake 

 Winnipeg, T. C. Weston, 1884 : three specimens from Jack Fish Bay, and one from each 

 of the other localities. 



Swampy Island, Lake Winnipeg, J. B. Tyrrell, 1880 : seven specimens. 



Cyrtocekas Manitobense. (N. Sp.) 

 (Plate XIII, figs. 3 and 4, and Plate XV, fig. 4.) 



Shell very slightly curved, slender, elongated and narrowly subfusiform, moderately 

 inflated a little in advance of the mid-length, though the dorsal margin, in a full lateral 

 view, is much more convexly curved than the ventral ; posterior extremity narrower and 

 more pointed than the anterior ; body chamber short, occupying less than one third of 

 the entire length, and narrowing gradually to the somewhat oblicjuely truncated anterior 

 end ; aperture rather large, simple and open, with a broad and shallowly concave constric- 

 tion immediately behind it, but only on the ventral side ; outline of a transverse section 

 through the broadest part ovate, the dorsum being narrower than the venter. 



Surface of the test on the sej)tate portion longitudinally ribbed. 



Suturai lines concavely arched on the sides, produced into moderately elevated and 

 simple saddles on the dorsum, and into similar but less prominent saddles on the venter. 



