CEPHALOPODA. 779 
Cameroceras hennepini.] 
upward termination of the continuous siphonal sheath, there is a sudden increase in 
the depth of the air-chambers. 
The marginal or submarginal portion of the sipho explains the obliquity of the 
septal annulations upon this tube, and the gentle incurvature of the septal funnels, 
the annulation of this tube. There is nothing in the material in hand to indicate 
any essential differences from the New York specimens of this species. 
Formation and locality.—The majority of the examples examined are from the Trenton limestone of 
Cannon Falls, Minnesota, and are from the collection of the late W. H. Scofield. The large siphon figured 
is from the same horizon at Wykoff, Minnesota (collection of Dr. C. H. Robbins), and other fragments 
from Decorah, Iowa. 
CAMEROCERAS HENNEPINI, Sp. nov. 
PLATE LII, FIGS. 1-3; PLATE LIII, FIGS. 1—3. 
This a fine large species, the most complete of the fragments which represent 
it indicating a length of not much less than four feet, with shell very gradually 
expanding. In a distance of 230 mm. the transverse diameter increases from 94 to 
100 mm. In section the shell is subelliptical being perceptibly flattened on the 
siphonal side, and less so on the opposite side, while the lateral curves are compara- 
tively narrow and abrupt. The air-chambers are relatively narrow, those exposed 
averaging about 20 mm. in depth, without increasing in this respect toward the 
upper extremity. There are fourteen of these chambers in a length of 270 mm. 
The sutures are not regular and simply transverse in their direction, but upon 
the siphonal side make a broad retral curve along the median line, bending forward 
again for one-third to one-half the depth of a chamber on the sides, but upon the 
antisiphonal side being more directly transverse and without curvature. The septa 
are very deep, sloping with broad, gently concave, almost, at times, plane surfaces 
to the sipho, about which there is a constriction. The sipho is very large, measuring 
46 mm. in diameter where the septum is 90 mm. In the lower portions of the 
specimens a distinct and continuous siphonal sheath is retained. The vertical 
section of a fragment represented on plate imu, fig. 1, shows the thickness of the 
siphonal wall, which has been preserved only on one side, the other having been 
destroyed in the process of fossilization. It is here seen that the mode of union of 
the septa to the sipho is a firm adhesion of the former to the outer wall of the latter, 
the septa being slightly thickened at their junction therewith. The structure of the 
shell substance shows with clearness that however firm the coalescence of these parts 
the distinction between the two is sharp. The specimen also shows the excentric 
position of the sipho, the shell not being much abraded on the siphonal side, but 
having lost considerably on the other side. 
