Secrion IV., 1902 [ 93 ] Trans. R. S. C. 
III.— Notes on Cambrian Faunas. 
By G. F. Marruew, LL.D. 
Earlier ‘“‘notes’’ were published in these Transactions in 1897-98 and ’99. 
(Read May 27, 1902.) 
No. 5. OBoLôID SHELLS OF THE CAMBRIAN SYSTEM IN CANADA 
AND THEIR RELATIONSHIP. 
Much has been done of late years to make known to us the type 
of Eichwald’s genus Obolus, and especially through the monograph 
on this genus prepared by Michwitz. Through his writings we now 
know the main points of the internal anatomy of that genus as pre- 
sented in the type species O. Apollonis and its variety Quenstedti, and 
can see how easily it might be misunderstood from the older repre- 
sentations of its form and internal features. 
Depending, as the paleontologists have had to in the first case, 
on external features as the means of determining the genus, a 
number of species have been referred to Obolus, which, when better 
known, were found to exhibit important points of difference, these 
were chiefly in the moulding of the interior surface of the valves. 
Of this moulding of the interior, the most distinctive markings 
are those which indicate the points of attachment of the muscles that 
move the valves, and the impressions of the main trunks of the 
circulatory system. Much variation was found in these two sets 
of markings, showing radical differences in the arrangement of the 
internal parts of the animal. Yet the more obvious characters of the 
external form, and the surface markings of the valves, are those which 
must necessarily first be used in assigning the species to its genus. 
We propose in this brief note to point out some distinctions 
which have been made out from a knowledge of the internal char- 
acters of the shells of the Oboli of the Cambrian System in Canada; 
and indicate some possible relations to other genera of shells that 
have been assigned to the genus Obolus. 
The species are referred to in succession, taking the oldest first, 
and continuing with those that are found in successively higher 
horizons in the Cambrian. 
