62 TRANSACTIONS OF THE ROYAL CANADIAN INSTITUTE. [VOL. XI 
external position. Between the carina and the suture there is a distinct 
concavity followed by a gentle convexity. The whorls of the spire are 
largely hidden by the lower whorls, and the exposed portion shows only 
a gentle convexity with slight if any evidence of the carina. 
The cast shows, in a much less distinct manner, the features given 
above. Near the aperture the carina and the superior concavity are 
visible, but about half way around the body whorl these features are 
obscured and the upper surface is flat, sloping gently upwards to the 
suture. The whorls of the spire are rounded and show no trace of 
angulation. 
The generic position of a shell in which aperture, umbilicus and 
slitband are not observable must of necessity be doubtful. The outline 
of the body whorl suggests the genus Helicotoma, but the failure of the 
carina on the whorls of the spire is a departure from this genus. The 
form of the shell is also remarkably like that of Euwomphalus precursor, 
Lindstrém!; in fact the only differences are the more marginal position 
of the elevated ridge and its apparent failure on the whorls of the spire. 
Ulrich regards E. precursor as marking a stage in the development of 
Ophileta into the typical Euomphalidae. It would appear, therefore, 
that our species represents either a degenerate type of Helicotoma 
extending into the Silurian, or a species of primitive Ewomphalus allied 
to E. precursor. On the whole the latter conclusion is probably better 
justified, but our material is much too imperfect to warrant definite 
statements as to generic position. 
In the preliminary report this species was referred provisionally to 
Trepospira kokeni, Lindstrém sp. A more detailed study has induced 
me to alter my opinion as above. 
Locality—Limestone rapids, Severn river, District of Patricia, Ontario. 
Horizon—Silurian. 
No. 396 S. Royal Ontario Museum of Palaeontology. 
EUOMPHALUS, sp. indet. 
Plate VII, Figure 1o. 
A single cast of the interior of a discoidally wound shell about 43 mm. 
in diameter. Three whorls are shown. The section of a whorl shows 
a generally rounded outline with a superior flattening and a peripheral 
angulation above the mid-height. The umbilicus is wide open and 11 mm. 
deep. The upper surface was probably very nearly flat or possibly 
slightly elevated. 
There can be little doubt that this form belongs to Euomphalus, but 
the specimen is too poorly preserved to warrant a specific name. The 
1 Sil. Gast. and Pter. of Gotland, p. 140, pl. XVIII, figs. 9-11. 
