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AUG. F. FOERSTE 
lengthwise curvature of the dorsal side is greater than that of the 
ventral side, and the siphuncle is close to the ventral side, but 
not in contact with the latter. In this position the siphuncle is 
said to be endogastric. The segments of the siphuncle present 
concave vertical outlines within the camerae, as well illustrated 
by Ruedemann. The septal funnels curve backward a distance 
equal to one camera. 
Only two species of Cyclostomiceras are known : cassinense 
(Whitfield) and C. miniwMm (Whitfield) ; both are confined to 
the Canadian (Beekmantown) of Vermont. 
The relationship of Cyrtoceras aristides Billings, of Canadian 
age, can not be determined in our present knowledge of that 
species. The living chamber apparently contracts toward the 
top somewhat as in a small Cyclostomiceras, but the siphuncle is 
rather large. Although the siphuncle is known to be in contact 
with the ventral wall of the conch, it is not possible to determine 
from the type in its present condition, imbedded in the matrix, 
whether its location is endogastric or exogastric. Nothing is 
known about the structure of the siphuncle. 
9. EXOGASTRIC CYRTOCEROIDS OF CANADIAN AGE 
The conch of Cyrtoceras confertissimum Whitfield is distinctly 
curved lengthwise and depressed dorso'-ventrally. The siphuncle 
is near the convexly curved side of the conch. According to 
Ruedemann^® the septal necks are short and the siphuncular seg- 
ments are nearly tubular, but very slightly contracted within the 
camerae. This concave outline of the siphuncular segments is 
characteristic of the numerous species referred to Oidhoceras, by 
Billings and other authors, in Canadian strata. The dorso-ven- 
tral depression of the conch, however, is a feature not seen in 
these so-called Orthoceroids, 
In Cyrtoceras alethes Billings, which may be of Ozarkian 
rather than of Canadian age, the conch is moderately curved 
lengthwise and strongly compressed laterally. The ventral side 
has a radius of lengthwise curvature of 25 mm. and a radius of 
lateral curvature of 3 mm. Only 6 camerae are present. If the 
lengthwise curvature of the ventral side continued along the liv- 
ing chamber the latter would be contracted dorso-ventrally, some- 
what as in the species described by Billings from the Black 
^ Ruedemann, R., Cephalopoda of the Beekmantown and Chazy forma- 
tions of the Champlain basin; New York State Museum Bull. 90, p. 507, 1906. 
