CEPHALOPODA. 243 



the septa in the latter is greater, and the siphuncle is expanded between the 

 septa. The organic deposit is very similar in the two species. 



Formation and localities. In the Schoharie grit at Schoharie, and the Hclder- 

 berg mountains, N. Y. 



Orthoceras obliquum, n. sp. 



PLATE LXXVm, FIGS. 1-4.. 



Shell straight, robust, transverse section subcircular. Tube regularly and 

 somewhat rapidly expanding from the apex. Apical angle from 9° to 10°. 

 Initial extremity unknown. 



Chamber of habitation very large, regularly expanding to the aperture. 

 Tlie cast of the interior is smooth. Aperture not observed. The air-cham- 

 bers numerous and shallow, having a depth of from one-sixth to one-seventh 

 of the diameter of the tube, or from three to five mm. 



Septa thin, smooth, with a small areola around the insertion of the 

 siphuncle. The suture line is curved on two of the sides, and very oblique 

 over the other two sides. The arc of curvature of the septa, measured from 

 specimen, fig. 3, is about 130°. The small specimen, fig. 4, apparently 

 belongs to this species, but is much flattened, and the curvature of the 

 septa destroyed. 



Siphuncle subcentral, small, diameter at the septa equal to about one- 

 third the depth of the chamber. The character of the siphuncle in its 

 passage between the septa has not been observed; one longitudinal section 

 indicates that it was probably expanded or moniliform. 



The largest fragment has a length of 220 mm., and a diameter of fifty 

 mm., at a point near the aperture. None of the specimens referred to this 

 species preserve any evidence indicating the thickness and ornamentation of 

 the test, — all being in the condition of casts of the interior. 



This species somewhat resembles 0. fluctum, but is distinguished by its 

 more rapidly enlarging tube, the greater obliquity and lesser curvature of the 

 septa; which are also more convex than in that species. In its vertical 



