CEPHALOPODA. 259 



This and the succeeding species are the only small forms observed from the 

 Schoharie grit. O. carnosum is distinguished by its size, the slightly ventricose 

 appearance of the chamber of habitation, and the surface characters. 



Formation and locality. In the Schoharie grit at Schoharie, N. Y. 



Orthoceras varum, n. sp. 



PLATES LXXJX, K1GS. 2, 1 ; AND CXII, FIGS. 5, 6. 



Shell straight, slender, subfusiform, point of greatest transverse section near 

 the base of the chamber of habitation. Transverse section broadly elliptical 

 or subcircular. Initial extremity unknown. 



Chamber of habitation gibbous, contracting rapidly toward the aperture, 

 where it is slightly expanded ; length more than twice the diameter at the 

 base. The anterior extremity is usually flattened, giving the aperture the 

 appearance of Gomi-hoceras. Much of this feature is probably due to com- 

 pression, but it is distinctly shown in nearly all of the individuals referred 

 to the species. Air-chambers regular, having a depth of from three to 

 four mm. 



Septa smooth, oblique, concavity nearly equal in depth to that of the 

 chambers. Sutures oblique, slightly curving. 



Siphuncle observed only at its insertion in the septa, where it is small, 

 having a diameter of one mm. ; the diameter of the shell at that point being 

 fifteen mm. 



Test and surface-markings not observed. 



The cast of the interior is smooth, with the sutures moderately impressed. 



Mature individuals of this species have had a length of about eighty mm. 

 One specimen having ten air-chambers and the greater portion of the grand 

 chamber, has a length of sixty-five mm. A smaller individual, with the 

 outer chamber and nine of the air-chambers, measures fifty-five mm. in 

 length. The smallest example of the species observed has a length of 40 

 mm., with a diameter of eleven mm. at the chamber of habitation. 



