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 O. 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, ITO8. 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 beyond 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-third the 

 diameter of the tube, or equal to an arc of 132°. 



Siphuncle central, having a diameter of five mm. where it penetrates the 



