CEPHALOPODA. 807 
Cyrtoceras houghtoni.] 
can be suggested is the somewhat greater interval between the lamellie and their 
stronger ventral curvature in the Canadian example. 
Formation and locality.—Trenton limestone, in the vicinity of Cannon Falls, Minnesota. Collec- 
tion of W. H. Scofield. 
CYRTOCERAS HOUGHTONI, sp. nov. 
PLATE LIX, FIGS. 12—15. 
Shell small, short, slightly arcuate, very compressed laterally, the dorso-ventral 
diameter being from one and a half to twice the lateral diameter. Dorsal surface 
obtusely rounded, ventral margin subacutely convex. Transverse section narrowly 
and rather acutely ovate. Greatest diameter of the tube, just behind the aperture, 
about twice that at the 16th septum. Body-chamber moderately deep, not direct 
but sharing in the general arcuation of the shell. Septa moderately, somewhat 
irregularly distant. Sixteen of the air-chambers have a length of 16 mm. on the 
sides, with a scarcely perceptible upward curve on the dorsum, and a broad ventral 
saddle which may be subacutely angled. Greatest convexity at the base of the 
body-chamber which is somewhat contracted toward the aperture. Sipho dorsal, 
submarginal. Surface covered with fine striz which over the body-chamber, are 
curved backward. A specimen 39 mm. in length on the venter has a body-chamber 
15 mm. deep. In one 45 mm. in the same dimension, the body-chamber is 20 mm. 
long. This specimen has the body-chamber entire. 
In this species the great lateral compression of the shell is the primary dis- 
tinguishing character. This added to the arcuation of the body-chamber and the 
very slight convexity of the septa renders the species readily separable from other 
described forms. 
Formation and locality.—Four specimens of this shell from the Trenton limestone of Cannon Falls, 
Minnesota, occur in the material loaned by the late W. B. Scofield. 
CyRTOCERAS FEATHERSTONHAUGHI, Sp. 10v. 
PLATE LVIII, FIGS. 12-15. 
Shell small, slightly arcuate, gently contracted at the aperture, expanded a 
little on the body-whorl and tapering toward the apex in low, convex curves. 
Dorsal or inner surface very depressed convex, rounding rather abruptly at the 
sides to a somewhat elevated venter. Transverse section broadest laterally. 
The greatest lateral diameter of the septum divides the major axis into parts 
which are as 2 to 3, the greater being ventral, Each septum is gently concave, the 
concavity being the most pronounced on the ventral slope. Air-chambers closely 
appressed, thirteen of them measuring 15 mm. on the dorsal side and 23 mm. on 
if 
