204 
AUG. F. FOERSTE 
6. CLAR-KOCERAS RUEDEMANN 
Genotype: Piloceras newton-winchelli Clarke, Geol. Minnesota, vol. 3, 
pt. 2, 1897, p. 767, figs. 8, 9; pi. 47, figs. 1-3. Ruedemann, New 
York State Mus. Bull., 80, 1905, p. 337 
Clarkoceras proclaims its relationship to the suborder Holo- 
choanites not only by the presence of endocones but also by the 
concave outline of the segments of the siphuncle within the 
camerae. The septal necks apparently extend the length of one 
camera. Excellent figures of the structure of the genotype are 
presented by Clarke. The siphuncle is free from contact with 
the adjacent wall of the conch. 
Clarkoceras holtedahli Foerste,^^ from the Canadian of Bache 
peninsula on Ellesmereland, evidently is congeneric. Here also, 
the elongated septal necks present concave vertical outlines with- 
in the camerae, as in Piloceras. The siphuncle is almost in con- 
tact with the adjacent wall of the conch. 
A similar structure is displayed by the species Cyrtocerina 
mercurius Billings (Plate XLI, Fig. 8), described from the Ca- 
nadian at Point Lewis, opposite Quebec, This species is related 
to, but is not congeneric with Clarkoceras. 
Typical Cyrtocerina (Plate XLI, Fig. 9), however, as repre- 
sented by its genotype Cyrtocerina typica Billings, from the 
Black River (Leray) at Pauquette Rapids, Ottawa river, Canada, 
belongs to the group Ellipochoanida, as originally defined by 
Hyatt. This group included both the suborder Orthochoanites 
and Cyrtochoanites as defined later in Zittel-Eastman’s Textbook 
of Paleontology. Judging from the convex curvature of the seg- 
ments of the siphuncle within the camerae, the relationship of 
typical Cyrtocerina is with the Cyrtochoanites. 
Among the various species described by Billings from the Ca- 
nadian strata of Canada under the name Orthoceras, there are 
two which evidently are related to Clarkoceras, although their de- 
gree of relationship can not be determined until the conch, as a 
whole, is known. These species are Orthoceras missiquoi and 
Orthoceras edax. 
In Orthoceras missiquoi the siphuncles are slightly curved, 
especially toward the apical end. That side of the siphuncle 
which is concavely curved lengthwise is smooth and a little flat- 
” Foerste, A. F., op. cit., pi. 27, figs. 2A, B; pi. 33, fig, 1. 
“ Hyatt, A,, Genera of fossil cephalopods; Boston Soc. Nat, Hist., Proc., 
vol. 22, p. 260, 1883. 
