72 
The strongly ventrad location of the siphuncle would oppose the 
reference of this specimen to Trockolites were it not for the fact that in the 
Trocholitidae the siphuncle starts ventrad of the centre, but becomes- 
dorsad of the centre in later stages of growth. Since the fragment may 
represent only an early stage of growth it is possible that at later stages- 
the siphuncle may have shifted toward the dorsal side of the conch. 
In a similar manner, the absence of an impressed zone is unfavourable 
to the reference of this specimen to the Trocholitidae, but this impressed 
zone may have developed later. 
The surface of the conch is striated transversely with sharply defined 
raised lines which are farther apart on the ventral side of the conch. It is 
estimated that about six stria occur in a length of 2 mm., where the 
diameter of the conch is 5 mm. On the ventral side of the whorl these 
transverse stria curve backward so as to locate former successive positions 
of the hyponomic sinus. The sides of the latter diverge at 152 degrees 
from each other. On the dorsal side of the whorl the stria are strictly 
transverse. 
Locality and Horizon. From the southern part of the North arm, 
Great Slave lake; in the same chert fragment as that containing the 
depressed Orthoceras described in the preceding lines. Collected by 
George S. Hume, Geological Survey, Canada. 
Remarks . The possibility of future identification of this small 
fragment with larger specimens rests chiefly on the curvature of the septa 
and the surface ornamentation of the shell. If a more mature specimen 
could be secured the generic position of this species probably could be 
determined readily. Its reference to Trocholites , in our present meagre 
knowledge of the species, is merely tentative. 
