200 
AUG. F. FOERSTE 
Canadian, in brief, is characterized by the dominance of holo- 
choanitic cephalopods, and the early Ordovician by the influx of 
numerous Orthochoanitic and Cyrtochoanitic cephalopods. 
It should be noted that in some of the Canadian genera of 
cephalopods, here cited as having concave vertical outlines, this 
concavity is so faint that their outlines are described more 
readily as straight than concave ; but they are distinctly not con- 
vex. This is true, for instance, of the species originally described 
as Cyrtoceras quebecense. 
2. SMOOTH ORTHOCONIC CANADIAN CEPHALOPODS 
Most of the smooth orthoconic cephalopods found in the Ca- 
nadian strata in Canada have the siphuncle in contact with the 
ventral wall of the conch. The sutures of the septa of Orthoceras 
sordidum Billings curve downward distinctly on the ventral 
side of the conch, as in the specimen figured by Ruedemann® from 
Fort Cassin, Vermont, under the name Endoceras montrealense. 
The septal necks extend downward the length of one camera 
and present a concave vertical outline within the camerae. Simi- 
lar septal necks are found in Orthoceras montrealense Billings 
and Orthoceras glaucum Billings. These species are alike in the 
small height of their camerae. In this respect they resemble 
Ellesmereoceras scheii Foerste, to which they miay be closely 
related. 
In Orthoceras indagator Billings the structure of the siphuncle 
is more like that of typical Endoceras. While the general ver- 
tical outline of the septal necks is concave within the camerae, 
the lower end of these necks curves inward to invaginate within 
the upper part of the neck next beneath. The upper part of the 
siphuncle of one specimen, numbered 7454 in the Victoria Me- 
morial Museum, appears to contain an endocone. Apparently 
Orthoceras ind.agator is one of the earliest known forms of typi- 
cal Endoceras , a genus common in the Chazyan. 
Nothing is known of the structure of the septal necks in Ortho- 
ceras sayi, O. autolycus, 0. veterator or 0. perseus, all described 
by Billings from Canadian strata, with the possibility of 
0. autolycus having been derived from Ozarkian strata, since it 
occurs in conglomeratic layers. Of these species, Orthoceras sayi 
has such a large siphuncle that it resembles typical Endoceras in 
® Ruedemann, R., op. cit., p. 424. 
