CEPHALOPODA. 415 



Chamber of habitation large ; length about twice its diameter at the base, 

 slightly contracting at the aperture, its capacity at least twice as great as all 

 the septate portion of the shell. Aperture at right angles with the direction 

 of the tube, slightly curving toward the apex on the convex ventrum. Air- 

 chambers regular, gradually increasing in depth toward the grand chamber, 

 and on the convex side increasing from a depth of six to nine mm. in the 

 distance of nine chambers. 



Septa regular, somewhat distant; nine in the space of fifty mm., as meas- 

 ured on the convex side of the outer volution, from the base of the grand 

 chamber. Suture lines not deeply impressed. Siphuncle below the centre, 

 on the concavo-dorsal side. 



Test imperfectly preserved in the specimens examined, consisting mainly 

 of the inner, macerated laminae attached to the cast. The exterior surface 

 has been marked by distinct, somewhat irregular, lamellose striae of growth, 

 which are crowded in folds toward the margin of the aperture. These have 

 been crossed by fine, somewhat distant and irregular, elevated, radiating or 

 revolving striae, which, on some parts of the shell, give a regularly cancel- 

 lated surface. 



The interior cast is essentially smooth, preserving remains of the surface- 

 markings, which are chiefly indicated in the transverse striae. One speci- 

 men has a diameter of seventy-two mm., and a transverse diameter of the 

 tube, near the aperture, of forty mm. 



This species bears much general resemblance to N. bucinum, but is distin- 

 guished by its slightly re-entrant or embracing inner volutions, its more nearly 

 circular transverse section, its less rapidly expanding tube, with comparatively 

 more distant septa, and by its surface characters. From N. liratus, in all its 

 varieties, it is more decidedly separated by the character of its surface- 

 markings. 



Formation and locality. This species is known only in the arenaceous shales 

 of the Hamilton group, near Cazenovia, N. Y. 



