810 THE PALEONTOLOGY OF MINNESOTA. 
[Cyrtoceras shumardi. 
The septa are very gently concave and closely appressed, the air-chambers 
being somewhat deeper on the venter than on the dorsum. Six of these septa 
occupy a length of 9mm. Sipho ventral and submarginal. 
The entire length of the specimen on both ventral and dorsal surfaces is 26 mm. 
of which 17 mm. belong to the body-chamber. 
Formation and locality.—In the upper buff beds of the Trenton series at Rockton, Llinois. 
CyRTOCERAS SHUMARDI, sp. nov. 
PLATE LX, FIGS. 1—4. 
The body-chamber and last air-chamber of a single specimen indicate the 
presence of another undescribed species of this genus, distinctly characterized by 
the very broad, somewhat flattened venter, narrow sides and broad, concave 
dorsum. This shape gives to the cross-section of the shell the form of a transverse 
oval somewhat flattened on one (the ventral) side. Another leading feature is the 
regularity of the suture which is without evidence of lobe or saddle even on the 
ventral side. The septum is deeply concave, its point of greatest convexity being on 
the dorsal side of the center. The aperture is slightly expanded, oblique and 
highest on the ventral side. The length of the body-chamber in this specimen is 
25 mm. The major and minor diameters of the aperture are 25 and 23 mm.; the 
major and minor axes of the last septum, 19 and 15 mm.; the depth or concavity 
of the last septum, 4.5mm. There is also a second specimen from near the apex 
of the shell, which retains the proportions of that described but has a greater 
arcuation of the conch. 
Formation and locality.—In the Trenton limestone at Cannon Falls, Minnesota. Collection of 
W. H. Scofield. ; 
CYRTOCERAS SCOFIELDI, Sp. /0U. 
PLATE LIX, FIGS. 9-11, 
A very sharply defined internal cast, which resembles in some respects 
Cyrtoceras camurum Hall, though with a more arcuate shell and more oval cross- 
section, retains a portion of the body-chamber with eleven air-chambers attached. 
From C. camurum it differs in the sharper venter, in the presence of a low and 
obscure median ridge on the dorsum and in the form of the septal sutures, which 
may be described as follows: 
At the median ridge on the dorsum they make a small but distinct saddle; 
thence they slope laterally in a very low lobe, again making a slight forward curve 
at about one-third the distance across the shell. From this point they make a broad 
and gentle lobe which covers the remaining portion of the side. Toward the 
