20 TRANSACTIONS OF THE ROYAL CANADIAN INSTITUTE. [VOL. XI 
height from the umbilical edge to the inferior lateral angle—4o mm. 
Height from the superior external to the inferior internal edge—33 mm. 
Width measured at right angles to the outer sloping side—25 mm. 
These figures are slightly greater than those indicated in Plate VII, 
Figure 5, which is prepared from a section not passing close to the 
aperture. The form of the aperture differs from the cross section shown 
in the figure, as the inner lip is drawn out giving a more rectangular 
appearance to the top. 
The specimens show no evidence of lines of growth or external orna- 
mentation of any kind. 
The few and rapidly expanding whorls separate this species sharply 
from forms like M. magna, but this very feature suggests M. logan; 
in fact, the character of the coiling is so like that of M. logani, and 
the general resemblance of some of our forms is so striking that I was 
at first inclined to ascribe the specimens to that species. A further 
resemblance is shown in the greater height as compared with the width 
of the whorl, and even the convexity of the under side is presented, 
but probably in a less distinct manner, by M. logani.1 On the other 
hand there are some striking points of difference shown by our speci- 
mens—the straight outline of the outer aspect of the whorl, the sharper 
inferior lateral margin, and the very much wider umbilicus. Our speci- 
mens may be distinguished from M. bigsbyi by the greater convexity of 
the under sides of the whorls and the straighter lateral outline. The 
whorls seem to expand more rapidly than in M. bigsbyi, and the relative 
height of the whorl is greater. Schuchert recognizes M. crassa, Ulrich 
and Schofield in the Trenton of Baffin Land: although our form is 
similar, I cannot regard it as belonging to this species. 
Whiteaves describes a species of Maclurea from the second and 
third limestone rapids of the Nelson river which he compares with 
M. bigsbyi. This form, however, cannot be co-specific with our speci- 
mens, as Whiteaves emphasizes the fact that the whorl is one-third 
greater in width than in height. 
Locality—Lower rapids, Shamattawa river, Manitoba. 
Horizon—Ordovician. 
No. 351 S. Royal Ontario Museum of Palaeontology. 
1 Geol. Sur. Can., Palaeon. Decade I, p. 7, pl. I. 
? Geol, Sur. Can., Rep. 1878-79, p. 48 C, 
