AMERICAN PALEOZOIC CEPHALOPODS 237 
The number of camerae in a length equal to the lateral diameter 
of the conch, varies in different specimens. In the large speci- 
men described above, 7 camerae occur in this length, if measured 
along the ventral side of the conch. Specimens with 6 camerae 
in this length are more common, and a few specimens with 5 
camerae in this distance occur. Close study fails to show any 
specific differences accompanying this variation in the relative 
number of camerae. 
The sutures of the septa rise moderately from the dorsal 
toward the ventral side of the conch, the amount of this rise 
varying from slightly more than the height of one camera, along 
the ventral side, to about one and a half camerae. Along the 
lateral sides these sutures curve slightly downward, forming 
very shallow lobes, readily detected only toward the upper part 
of the phragmacone. Along the ventral side the sutures arch 
•moderately upward, producing low, broad saddles. The middle 
part of these saddles tends to be less curved than the lateral 
parts, and in some specimens there is a faint downward curve of 
the sutures along the median line of the ventral side, but this is 
by no means a constant feature. 
The septa are moderately concave, their curvature being 
greater dorso-ventrally than laterally. The siphuncle is located 
on the ventral side. Its distance from this side varies from one- 
fifth to two-sevenths of the dorso-ventral diameter. 
In the specimen from Flat Fork, (Plate XXXIV, Fig. 2), 
three and a half miles northeast of Oregonia, Ohio, the center of 
the siphuncle is 5.5 mm. distant, where the dorso-ventral diam- 
eter is 36 mm. The segments of the siphuncle vary from 5.5 to 
6 mm. in diameter dorso-ventrally, at mid-height of the camerae, 
diminishing to 4, or even 3 mm. where in contact with the septa, 
the passage through the septa being still narrower. Along the 
dorsal side of the siphuncle, the vertical outline of the segments 
is more evenly convex; but along the ventral side the vertical 
outline is distinctly convex above and concave below, the con- 
cave part being adnate to the septa beneath for a length of 3 to 
5 mm. The upper part of the dorsal outline of some of the seg- 
ments is adnate for a length of 1 to 3 mm. to the overlying septa, 
while in other segments no adnation is noted. The septal neck of 
this specimen appears to be very peculiar in construction. On 
the dorsal side of the siphuncle the septum maintains an even 
