THE TRENTON LIMESTONE OF MANITOBA. 83 



Black Island, Lake Wiunipeg, a little to the west of Swampy Island, two specimens ; 

 and at the south end of Swampy Island, about eight miles from Black Island, one speci- 

 men ; all three collected by Messrs. Dowling and Lambe in 1890. 



The specimen figured, which is from Black Island, has about three inches of the 

 chamber of habitation preserved and a little more than three inches and a half of the 

 septate portion. The specimen from Swampy Island, which is septate throughout but 

 imperfect at both ends, is five and a half inches iu length, by about thirty-six millimetres 

 in its maximum diameter at the larger end and twenty-nine at the smaller. 



ACTINOCERAS ElCHARDSONI, Stokes. 



Plate IX, figs. 1, 2, and 2a. 



Actinoceras Richardsoni, Stokes. 1S40. Trans. Geol. Soc. Lond., ser. 2, vol. v, pt. 3, p. 70S, pi. lix, figs. 2 and 3. 

 f Ormoceras Brongniarti. D. Dale Owen. 1852. Geol. Rep. Wiscons., Iowa and Minn., p. 181. 

 Aclinociras Lijom, Whiteaves. 1880. Geol. Surv. Can., Rep. Progr. 1878-79, pp. 460 and 48c, of Appendix 1. 

 Actinoceras Richardsoni. Foord. 188S. Cat. Foss. Cepb. Brit. Mus., Pt. 1, p. 172. 



" From Lake Wiunipeg, iu yellowish-white limestone much resembliug that from 

 Igloolik," Stokes. Probably from the first and second limestone points on the west side of 

 Lake Winnipeg, north of the Saskatchewan where it was collected by Sir John Richardson 

 on Franklin's fiist expedition in 1814 and subsequently by Captain Back in 1832. Lower 

 Fort Garry (Stone Fort) on the Eed Eiver, D. Dale Owen, 1848, Dr. Hector, 1857, Donald 

 Guun, 1858, Dr. Selwyn, 1872, Dr. R. Bell, 1879 and 1880, and T. ,C. Weston and A. 

 McCharles, 1884 ; apparently abundant. East Selkirk, T. C. Weston and A. McCharles, 

 1884. 



This species is represented in the Museum of the Survey by a fine series of specimens 

 from the Eed Eiver valley. These show that the rate of tapering in some specimens is 

 rather more rapid than has generally been supposed. Thus, in the original of fig. 1, on 

 Plate IX, in a length of four inches the maximum diameter of the shell increases from 

 thirty-seven millimetres at the smaller end to sixty at the larger. The outline of a trans- 

 verse section is usually circular, except when the specimen has been abnormally com- 

 pressed. The surface markings consist of rather regularly disposed transverse and imbri- 

 cating striae. The septa, as described by Mr. Foord, are " four lines distant where the 

 shell has a diameter of three inches," and arch strongly forward and outward. The very 

 large, submarginal and nummuloidal siphuncle varies in its proportionate size in different 

 specimens, though its maximum diameter is usually more than half that of the shell. It 

 is very strongly inflated between the septa and both acutely and narrowly constricted at 

 the places where they join it. In the longitudinal section of a specimen of this species 

 represented by figure 2 of Plate IX, the posterior segment of the siphuncle is thirty-six 

 millimetres in maximum breadth and nine in height, while the last perfect segment 

 anteriorly is forty-seven mm. iu its greatest breadth, by ten in height. The endosiphon 

 and the lateral tubuli which proceed from it, are all well shown in this and other similar 

 sections. 



Figures 3 and 3a, on Plate IX, represent the apical extremity of what appears to be 



