ARCTIC ORDOVICIAN AND SILURIAN CEPHALOPODS 263 
The type of Cyrtocerina, namely Cyrtocerina typica, is from the 
Leray division of the Black River at Pauquette Rapids, on the 
Ottawa River, in Canada, A second species, Cyrtocerina mer- 
curius, was described by Billings from the Levis division of the 
Canadian at Point Levis, in Quebec, Canada. A third species, 
now known as Cyrtocerina madisonensis , was described by Miller 
from the Saluda member of the Richmond at Madison, Indiana, 
and a fourth species, Cyrtocerina (?) schoolcrafti, was described 
by Clarke from the Decorah division of the Black River near 
Cannon Falls, Minnesota. It is not certain that all of these are 
congeneric. 
Among all these species, the relationship of the Victoria Head 
species described above, under the name Clarkoceras holtedahlij. 
appears nearest to the Canadian genotype, Clarkoceras newton- 
winchelli, thus favoring the Canadian age of the enclosing strata 
at Victoria Head. 
3. Eremoceras syphax (Billings) 
Plate XXXIII j figs, 8 Aj B, C; fig, 2 
Cyrtoceras syphax Billings, Pal. Foss., 1, Geol. Surv. Canada, 
1865, p. 194, text fig. 178. 
Eremoceras syphax Hyatt, Proc. Boston Soc. Nat. Hist., 
22, 1884, p. 282, Genotype. 
Type specimen. — Conch slightly curved lengthwise along its 
dorsal side, the radius of convex curvature of the latter being 
about 100 mm. The ventral side is either straight or too faintly 
concave to be measured for curvature, at least in the type speci- 
men. This specimen consists of the living chamber with 11 
camerae and part of a twelfth camera still attached. The height 
of the living chamber is 18 mm. along its dorsal side; the margin 
of the aperture slopes gently downward from the dorsal toward 
the ventral side, so that the height of the living chamber along its 
ventral side is estimated at about 15 mm. The upper part of the 
shell of the living chamber is thickened slightly interiorly for a 
distance of 8 mm. from the aperture. On the cast of the interior 
of this chamber this thickening of the shell is indicated by a 
slight constriction of the upper part of the cast. 
