240 PALAEONTOLOGY OF NEW YORK. 



margins, and the curvature unsymmetrical. All the specimens referred to 

 this species agree in this feature of the septa. Figure 3, of the same plate, 

 resembles this species, except in the greater distance between the septa. The 

 view of the specimen represented is the much flattened and weathered dorsal 

 side. The ventral side of the specimen is less compressed, and shows the septa 

 to be slraight and horizontal; the air-chambers are grooved and ornamented 

 by a longitudinal carina, as partially represented in figure 2 of 0. cingulum. In 

 some of its phases this species resembles 0. luxum ; but the septa are more 

 closely arranged, and the position and character of the siphuncle is quite 

 different. In its vertical distribution this species is not known beyond the 

 limits of the Schoharie grit, and its geographical distribution is confined, so 

 far as at present known, within the counties of Albany and Schoharie. 



Formation and localities. In the Schoharie grit in Schoharie, and at the base 

 of the Helderberg mountains, N. Y. 



Orthoceras cingulum, n. sp. 



PLATE LXXVI, FIGS. 2, 3. • 



Shell straight, regularly and gradually enlarging. Transverse section, judging 

 from the degree of compression, subcircular. Apical angle varying in com- 

 pressed specimens from 6° to 8£°. Initial extremity unknown. 



Chamber of habitation having only a small portion of the base preserved 

 in the specimens examined; the internal cast of this portion is smooth, and 

 very gradually enlarging. Air-chambers numerous, regularly increasing in 

 depth from the apex of the specimen to the chamber of habitation, varying 

 in depth from five to ten mm. in the space of 140 mm. Internal cast of 

 the walls essentially smooth, except at the base of each chamber in 

 weathered specimens, where the produced septal margins are dissolved, 

 giving the specimens a peculiar banded or zoned appearance. 



Septa horizontal and straight on the margins, presenting a rigid appear- 

 ance in specimens not disturbed by compression ; marked by a raised areola 

 around the insertion of the siphuncle, which is surrounded by vascular 

 markings. 



