24 TRANSACTIONS OF THE ROYAL CANADIAN INSTITUTE.  [VOL. XI 
Our specimen is a fragment of the camerate shell about 120 mm. 
long: it is 65 mm. in diameter at the anterior end, and 47 mm. at the 
posterior extremity. It is possible, but not certain, that the shell was 
somewhat elliptical, measuring 65 by 50 mm.anteriorly and 47 by 40 mm. 
posteriorly. The rate of tapering indicated by these figures agrees 
fairly well with that given for A. bigsbyi. The external characteristics 
of the shell are not well shown, but it is probably smooth. I am unable 
to see ‘‘the longitudinal, undulated, fine, thread-like lines’’ of Hall. 
The septa are 10 mm. apart, strongly curved orad: they are thin and 
delicate in structure. 
The siphuncle is large, possibly 27 mm. in diameter at the smaller 
end of the specimen, but as some deformation has occurred, the exact 
diameter cannot be stated. The siphuncle is situated very close to one 
side of the shell. 
The structure of the siphuncular sheath is very exact and persistent. 
In vertical section the inner ends of the septa are seen to extend directly 
apicad, forming an annular funnel for half the interseptal distance. In 
the posterior half of the interspace the siphuncle swells out into evenly 
rounded rings. This definite structure is not emphasised by authors 
in the descriptions of A. bigsbyi, and on this account I was inclined to 
ascribe our specimen to some other species. Bigsby’s original figures, 
however, point strongly to this type of siphuncle.!. Barrande’s revision 
of the species shows that the swelling is located in the posterior part of 
the interseptal space, but his drawings do not emphasize the directly 
backward inflection of the septa into tubular necks.? 
The endosiphuncle is not preserved, but the whorls of radial tubuli 
(‘‘verticillations”’ of Stokes) are admirably preserved, and project from 
the inner sides of the nummuloidal rings almost at right angles. These 
structures must have been strongly calcified to withstand the vicissi- 
tudes to which the specimen has been subjected. The presence of these 
structures outweighs any objection based on the exact form of the 
siphuncular segments, which, considered alone, would suggest Orthoceras 
(Actinoceras) anticostiense, Billings, from the Upper Ordovician of Lake 
St. John (See plate 434, Figs. 9 and 10, Systéme Silurien de la Bohéme). 
My examination of this specimen has induced me, with great reluc- 
tance, to doubt Whiteaves’ recorded occurrence of the species at Lower 
Fort Garry. Ifthe form figured by Whiteaves is really A. bigsbyi we must 
entirely recast our conception of the species. (Royal Soc. Can., op. cit.). 
Locality—Lower rapids, Shamattawa river, Manitoba. 
Horizon—Ordovician. 
No. 308 S. Royal Ontario Museum of Palaeontology. 
1 Trans. Geol. Soc., ser. II, Vol. I, pl. XXV, figs. 1 and 2, 1824. 
2 Systéme Sil. de la Bohéme, pl. 437, figs. 10-16, 1870. 
