222 



Shell elongated, slightly curved, narrowly subfusiform, but much nar- 

 rower at the posterior than at the anterior end : antisiphonal side gently 

 convex and broadly arched : siphonal side almost straight but faintly 

 concave. 



Septate portion conical : septa, as seen in a longitudinal section, rather 

 closely approximated, the sutures of the last twelve or fourteen averaging 

 from five to six millimetres apart : siphuncle large, occupying nearly one- 

 half the entire diameter in the broadest part, but narrowing rather 

 abruptly near the body chamber, nummuloidal, expanded between the 

 septa and placed near the margin of the concave side. 



Surface markings unknown. 



Little Black Island, Lake Winnipeg, D. B. Dowling and L. M. Lambe, 

 1890 : one specimen, which is much narrower in proportion to its length 

 than 0. magnum and not nearly so prominent or gibbous on the anti- 

 siphonal side, but it is doubtful whether it should be regarded as a mere 

 variety of that species or as a distinct species. 



Oncocehas Whitbavesii, Miller. 



Oiicoccras gihhosuui, Whiteaves 1889. Trans. Royal Soc. Canada, vol. VII., 



sect. 4, p. 80, pi. 15, figs. 2 and 3. But not 

 O. gi'obosum, Hall, 1852. 



If TFArtcnrfsiV, Miller 1892. First Append, to IC. Amer. Geol. 



and Palaeont., p. 697. 



Shell resembling that of 0. magnum in form, though perhaps a little 

 broader in proportion to its length, also in the characters of its interior, 

 but apparently always differing therefrom in its very much smaller size. 

 Thus, the smallest specimen of 0. m,agnum, known to the writer must 

 have been at least eight inches in length when perfect and the largest 

 fully eleven, whereas in the present species, out of twenty-seven speci- 

 mens collected, the smallest could not have been much 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. The surface markings of 0. magnum 

 are still unknown, but the surface of the test of the septate portion of 0. 

 Whiteavesii is marked with very small, low, faint, closely and regularly 

 disposed, straight, transverse ribs. 



Big Island, Washow Bay, Bull Head Bay, and Pike Head, Lake Win- 

 nipeg, T. C. Weston, 1884 : three specimens from Pike Head and one 

 from each of the other localities. ' Little Black Island, Lake Winnipeg, 

 J. B. Tyrrell, 1889, seven specimens, and D. B. Dowling and L. M. 

 Lambe, 1890, ten specimens. Little Tamarack Island, Commissioners' 

 Island, and Clark's Point, Lake Winnipeg, D. B. Dowling, 1890: one 

 specimen from each of these localities. North end of Big Island, D. B. 

 Dowling, 1891 : one specimen. 



