THE TRENTON LIMKSTOKE OF MANITOBA. 85 



AcTiNOCERAS Allumrttense, Billiugs. (Sp.) 

 Plate X, figs. 3 and 3a. 



Orthoceras AUumetfense, Billings. 1857. Geol. Surv. Canada, Rep. Progr. 1853-56, p. 331. 



" " Barranile. 1S70. Syst. Silur. de Bohême, vol. n, pi. ccccxxxvii, figs. 6-9. 



" " " 1874. lb., texte iii, p. 729. 



Lower Fort G-arry, Dr. R. Bell, 1880 : a single specimen, of which a longitudinal sec- 

 tion is figured. The specimen is a little more than six inches in length, by nineteen 

 millimetres in its maximum diameter at the smaller end and thirty-six at the larger. It 

 is here identified with the present species, with some confidence, after a careful compari- 

 son with four of Billings' types of O. Allumet/ense, from Paquette's Rapids, on the Ottawa 

 River. A specimen collected by Messrs. Dowling and Lambe at Black Bear Island, Lake 

 Winnipeg, in 1890, which consists of a natural but much weathered longitudinal section 

 of the shell, about eight inches in length, in a piece of rock, is also probably referable to 

 this species. 



A. Allumetlensc seems to be intermediate in its characters between Adinoceras and 

 Sacioceras, and should, perhaps, be referred to the latter genus rather than to the former. 

 Still, in the Or(hocera< Rklderi of Barrande, which is stated by l^rofessor Hyatt to be the 

 type of his genus Sndoceras, the height and breadth of the siphuncular segments, which 

 are moniliform rather than nummuloidal, are represented as nearly equal, whereas in 

 A. Allumellense these segments are nearly twice as broad as high, and therefore more 

 nearly nummuloidal. 



Sactoceras Canadense. (Sp. Nov.) 



Plate X, figs. 1 a-c. 



Shell narrowly elongated, rather slender, somewhat fiisiform, cyliudro-conical and 

 increasing veiy slowly in thickness from the posterior end to a short distance beyond the 

 midlength, thence narrowing slightly to the aperture ; length about six times greater 

 than the maximum thickness ; dorsal and ventral regions compressed, though perhaps 

 abnormally so, the outline of a transverse section through the thickest part, near to the 

 body chamber, being broadly elliptical. Septate portion, in the only specimen known to 

 the writer, occupying about two-thirds of the entire length, and divided into seventeen 

 chambers, its apical extremity obtusely pointed ; chamber of habitation nearly cylindrical, 

 though its maximum diameter is about six millimetres greater at its commencement pos- 

 teriorly than at the aperture. Surface markings unknown. Septa shallowly concave 

 externally in the dorsal and ventral regions, their distances apart averaging about one- 

 third the maximum diameter, except the two or three last formed, which are rather closer 

 together. Siphuucle, as seen in a longitudinal section of the specimen, eccentric, sub- 

 marginal, very large and much swollen between the septa posteriorly, but ultimately 

 much diminishing in size towards the chamber of habitation. At the apex, posteriorly, 

 nearly the whole of the first chamber is filled up with the first segment of the siphuncle, 

 which is twelve millimetres in its maximum diameter. In the next five or six chambers, 

 the siphuncular segments fill the greater part of the space, and average from fifteen to six- 



