223 



Cyhtoceeas Manitobense, Whiteaves. 



Ci/rtoceras Manitobense, Whiteaves 1889. Trans. Royal Soc. Canada, vol. VII., 



sect. 4, p. 80, pi. 13, figs. 3 and 4, and pi. 

 15, fig. 4. 



Shell very slightly curved, slender, elongated and narrowly subfusi- 

 form, moderately inflated a little in advance of the mid-length, though 

 the siphonal side, in a full lateral view, is much more convexly curved 

 than tljie antisiphonal ; 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 obliquely 

 truncated anterior end ; aperture rather large, simple and open, with a 

 broad and shallowly concave constriction immediately behind it, but only 

 on the antisiphonal side ; outline of a transverse section through the 

 broadest part ovate, the siphonal side being narrower than the anti- 

 siphonal. 



On the septate portion of most of t'le specimens collected, the surface 

 of the test is marked by low, rounded, longitudinal ribs, but in some 

 flattened fragments from Inmost Island, which are apparently referable 

 to this species, there are very distinct transverse crenate raised lines 

 between the ribs. 



Sutural lines concavely arched on the sides, produced into moderately 

 elevated and simple saddles on the siphonal side, and into similar but less 

 prominent saddles on the antisiphonal side. Siphuncle placed at a short 

 distance from the margin of the convex side. In the longitudinal section 

 of a specimen from Bull's Head figured on Plate 15 of the seventh 

 volume of Transactions of the Royal Society of Canada, the siphuncle 

 appears to be very slightly expanded between the septa. 



Dimensions of the most perfect specimen collected : actual length 

 along the median line of one of the sides, 129 mm.; estimated total 

 length of the same, when perfect, 133 '5 mm. ; maximum diameter of the 

 same, from the siphonal to the antisiphonal side, 34 '5 mm. ; greatest 

 lateral diameter 31-5. 



Big, Deer and Punk islands, Big Grindstone Point, Bull's Head, Dog 

 Head and Pike Head, Lake Winnipeg, T. C. Weston: two nearly perfect 

 specimens, one from Big Island and one from Bull's Head, those from 

 the other localities being for the most part only pieces of the posterior 

 and septate portion of the shell. 



Deer Island, Lake Winnipeg, J. B. Tyrrell, 1889 : the most perfect 

 specimen known to the writer. 



A fine specimen of a Cyrtoceras, collected by Dr. R. Bell in 1879 at 

 the second rapid of the Nelson Rivsr, Keewatin, may also be referable to 

 C. Manitobense, though it differs somewhat from that species in the size. 



