98 



reous coil composed of from twenty to thirty sinistral volutions, in close 

 contact (b), and this in its turn is enveloped in a thin calcareous outer 

 layer or sheath (c). The volutions of the outer of these two shelly coils are 

 flattened from back to front and narrow at the edges, so that in specimens 

 such as the originals of figs. 5 and 5 a, in which the thin outer coating is 

 not preserved, as is usually the case, it is only the outer edges of the volu- 

 tions that are visible. At the larger end, the outer layer or sheath, when 

 preserved, seems to project very slightly beyond the outer shelly coil and 

 to form a raised rim around it, but in those specimens in which the outer 

 layer is not preserved, the last volution of the outer coil appears to ex- 

 tend a little beyond the central axis, and to be ultimately truncated 

 rectangularly, thus giving the appearance of a comparatively broad de- 

 pression in the centre of the larger end, as represented by figure 5 a. 



CEPHALOPODA. 



Obthoceras Selwyni, Billings. 



Orthoceras Selwini, Billiiigs. 1862. Geol. Surv. Canada, Pal. Foss., vol. I., p. 161. 



Gait, Dr. R. Bell, 1861 ; a very imperfect cast of part of the interior 

 of the septate portion of the shell. The siphuncle is placed at a short 

 distance from the margin and apparently moniliform, like that of 0. 

 angulatum, Wahlenberg, as figured by Foord, (figs. 7, a-f) on page 71 of 

 the first part of his Catalogue of the Fossil Cephalopoda in the British 

 Museum, but the surface markings are unknown. The only other speci- 

 men of this imperfectly characterized species that the writer has seen is 

 an equally badly preserved cast of the interior of part of the septate por- 

 tion of the shell, collected at Elora by Mr. Townsend and kindly pre- 

 sented to the Museum of the Survey by Mr. B. E. Walker, of Toronto. 



Orthoceras crebescens. Hall. 



Orthoceras crebescens, Hall 1867. Twentieth Rep. Reg. N. Y. St. 



Cab. Nat. Hist., p. 354, pi. 19, figs. 



1, 2 and 3. 



Hall & Whitfield. 1875. Rep. Geol. Surv. Ohio, vol. II., pt. 



2, p. 148, pi. 9, fig. 2. 

 Whiteaves 1884. This volume, pt. 1, p. 37. 



Hespeler, T. C. Weston, 1871, and Elora, Mr. James Gladstone, 1876 : 

 the two specimens referred to on page 37 of the first part of this volume. 

 Both of these are coarse and imperfect casts of the interior of the shell, 

 upon which no traces of the surface markings are preserved. 



