CEPHALOPODA. 
323 
This species differs from G. fax in the size and character of the aperture, 
and apparently greater curvature of the shell. The characters of the aperture, 
and the point of greatest transverse section, also distinguish this species from 
the remaining associated forms. 
Formation and locality. In the Schoharie grit, at Schoharie, N. Y. 
Gomphoceras clavatum. 
PLATES XLVI, FIGS. 14, 15; XCIII, FIGS. 2, 3. 
Cyrtoceras clavatum. Hall. Illustrations of Devonian Fossils: Cephalopoda, pi. 47, flys. 12, 13. 1373. 
Shell curved; curvature endogastric. Considering the slope of the dorsal and 
ventral sides of the chamber of habitation, the curvature seems to be the 
reverse of that indicated by the chambered portion of the tube, which is 
clearly concave along the ventral side. Tube regularly and gradually enlarg¬ 
ing from the apex to the base of the chamber of habitation, and contracting 
rapidly to the aperture. Transverse section broadly oval, slightly flattened 
on the dorsal side. Apical angle about 22°. Apex acute. 
The chamber of habitation has a length equal to the greatest ventro-dorsal 
diameter of the tube. The tube is constricted at the aperture. The dorsal 
and lateral faces slope gradually toward the large aperture: the ventral 
side has a greater convexity, and slopes very rapidly to the margin of the 
small aperture. The crenulations have not been observed. 
Aperture suboval, small, having a diameter equal to about two-thirds the 
greatest lateral diameter of the tube. The small aperture is merely a slight 
bend or sinus in the margin from the large aperture, which is elliptical, and 
constitutes the principal feature of the entire aperture. 
Air-chambers regularly increasing in frequency from the apex to the outer 
chamber, and varying in depth from 2.5 to 4 mm. in the length of thirty 
mm. Occasionally the last one or more of the air-chambers are shallower 
than the preceding. Septa' with a concavity equal to the depth of the air- 
chambers. Sutures bending toward the aperture over the ventral and dorsal 
sides. 
