ARCTIC ORDOVICIAN AND SILURIAN CEPHALOPODS 283 
52 mm., the radius of transverse curvature of the ventral side 
is 50 mm., that of the dorsal side being estimated at 25 mm. 
At this larger end of the specimen the transverse curvature at 
the ventro-lateral angles has a radius of about 11 or 12 mm. 
Five earner ae occupy a length equal to the lateral diameter of 
the conch at the top of the series being counted. On the dorsal 
side, the sutures of the septa are directly transverse. On the 
ventral side these sutures curve downward, producing broad 
shallow lobes having a depth of 4 mm. at the base of the speci- 
men, increasing to 5 mm. at its top. The lateral curvature of 
these ventral lobes increases from 30 mm. at the base of the speci- 
men to 33 mm. at its top. The septum at the base of the speci- 
men slopes downward from the dorsal side toward the ventral 
side at an angle of about 82 degrees with the vertical outline of 
the ventral side. In fact, the structure of the phragmacone is 
similar to that of an ordinary species of Orthoceras in which one 
side had been filed away so as to produce a similar flattened 
outline. 
At its passage through the septum the siphuncle has a diameter 
of about 3 mm. The center of the siphuncle is slightly less 
than one-fourth of the dorso-ventral diameter of the conch 
from its ventral wall. The septal necks of the siphuncle are 
2 mm. in length and curve outward toward their lower margin. 
The connecting rings, which join successive septal necks, are 
preserved only on the ventral side of the siphuncle, but originally 
these rings appear to have enlarged to a diameter of about 6 
mm. within the camerae, producing segments of the siphuncle 
with vertically elliptical outlines as in Loxoceras, 
No indications of surface markings are present, the specimen 
being a cast of the interior of the conch. 
Locality and Horizon. — From blocks found loose at Port 
Burwell, twenty miles west of Cape Chidley, at the northern 
end of Labrador. Regarded as of Black River age on account 
of associated fossils, also loose. Collected by A. P. Low. Num- 
bered 7923 in the collections of the Geological Survey of Canada. 
