CEPHALOPODA. 
235 
from three to four in the space of thirty-five mm. Siphuncle central. One 
specimen, preserving the chamber of habitation and twelve air-chambers, has 
a length of 230 mm., with a diameter of seventy mm. at the largest part of the 
tube. The septa are more frequent than in undoubted 0. Pelops; but without 
more distinctive material, these forms from the limestone cannot be specifically 
characterized. 
Formation and localities . In the Schoharie grit at Schoharie, and at numerous 
localities in the Helderberg range, and in the outcrop of this formation along 
the Hudson River valley as far as Orange county, N. Y. It probably occurs 
in the same formation in New Jersey, as it appears to be coextensive with the 
Schoharie grit. 
Orthoceras Zeus, n. sp. 
PLATE LXXV, FIGS. 1-3. 
Shell robust, forming a straight, elongate cylindro-conical tube, which 
diminishes very gradually in receding from the chamber of habitation. 
Transverse section circular. The apical angle is about 8^°, measuring from 
fragments preserving the chamber of habitation and the lower septate 
portion. Initial point unknown. 
Chamber of habitation large, and subcylindrical, being about twice as long 
(in an imperfect specimen) as the diameter at its base, and very gradually 
expanding towards the aperture, below which it is marked by a wide, shal¬ 
low, curved constriction. Aperture unknown, but the tube is apparently 
gently expanded bejmnd the constriction. Air-chambers large. 
Septa thin, and distant from each other about one-fourth the diameter of 
the tube, or in actual distance, where the tube measures from fifty to sixty 
mm., they are about twelve mm. distant from each other. Surface of the 
interspaces, or casts of the interior of the chambers smooth, and flat on the 
exterior. Concavity of the septa equal to about eighteen mm., one-tliird the 
diameter of the tube, or equal to an arc of 132°. 
Siphuncle central, having a diameter of five mm. where it penetrates the 
