1915] PALAEOzOIC FossiLs FRoM HupsoNn Bay. ai 
MACLUREA ACUTA, Sp. nov. 
Plate VII, Figures 1 and 2. 
MACLURINA MANITOBENSIS ACUTA, Parks. Bur. Mines of Ont., 22nd Rep., pt. I, p. 190. 
The only specimen of this species has a maximum diameter of nearly 
100 mm. (The cast is 95 mm.). The vertical height of the deepest part 
preserved is 35 mm. Three whorls are shown, the inner one being 
extremely small. The under side is flat and slightly concave in the 
centre. The lower aspect of the whorls is very slightly convex, but 
this appearance would be greatly increased in the cast and the sutures 
would be quite deep. The actual width of the umbilicus is 18 mm. 
and its greatest width from summit to summit of the body whorl is 
35 mm. The inferior margin of the whorls is acute, with a slight but 
distinct depression just above the angle. The outer aspect shows a 
decided slant with a slight convexity to the summit of the whorl. The 
measurements of the cast of the outer whorl nearest the aperture are as 
follows: 
Vertical height—33 mm. 
Width on the flat side—35 mm. 
Width at right angles to the outer side—28 mm. 
Although the shell is very well preserved on the base there is no 
indication of lines of growth or of ornamentation. 
In the preliminary report this shell was made a variety of Maclurina 
manitobensis, Whiteaves,! which it strongly resembles in the character 
of the coiling and in the shape of the whorls. Although the aperture of 
our specimen is not shown, it is nevertheless fairly complete and indi- 
cates a much smaller size than that of WM. manitobensis, and although 
the shell is well preserved on the flat side there is no indication of the 
periodic arrests of growth mentioned by Whiteaves, nor is any sign to 
be seen of the revolving lines and transverse coste on the upper side, 
although a small portion of the shell is preserved. A comparison with 
specimens in the Royal Ontario Museum indicates a slightly greater 
rate of expansion in the whorls of the present example. I am by no 
means convinced that my original diagnosis was wrong, but as surface 
ornamentation is of prime importance in M. manitobensis, and as this 
ornamentation is not shown by our specimen, it is perhaps better to 
describe the present example as a distinct species, more particularly as 
Whiteaves’ species has been removed to another genus, Maclurina, on 
the basis of the structure of the operculum—a feature which cannot be 
ascertained for the present example. Maclurina manitobensis is common 
in the Trenton of Silliman’s Fossil Mount, Baffin Land, which is an 
additional argument for the identity of the present form. 
1 Trans. Royal Soc. Canada, Vol. VII, sec. IV, p. 75, pl. XII, pl. XIII, figs. 1 and 2. 
