CEPHALOPODA. 283 



toward the outer chamber, varying from three to five mm. in the length of 

 ninety mm. 



Septa and siphuncle not observed. Sutures curving and oblique, but 

 slightly impressed on the internal mould. Ventral side indicated by a longi- 

 tudinal carina along the cast of the chamber walls. 



The test has a thickness of nearly one mm. Its surface-markings are 

 unknown. 



The specimen figured has a length of 190 mm., and embraces more than 

 thirty of the air-chambers, with a portion of the chamber of habitation, 

 which has a diameter of thirty mm. near the aperture. 



This species is associated with 0. Marcellense in the Goniatite limestone of 

 the Marcellus shale, and is distinguished by its more frequent septa, the curved 

 and oblique sutures, and more gradually enlarging tube.- 



Formation and locality. From the Goniatite limestone of the Marcellus shale 

 at Manlius, N. Y. 



ORTHOCERAS 8UBULATCM. 



PLAT I - XWVIII, no. 3; I. XXXIV, FIGS. 1,2,4,6-10; LXXXVI, FIGS. 1, 2. 



Slender Orthocera, Vamixbm. Geolojf. Survey of N. Y. : Rep. Third Disk, p. 148. 1842. 

 (irtln>ceras suimlatttm. Hall. Oeolog. Borv. of N. Y. : Rep. Fourth Dist., p. 180, fig. 1. 1843. 



" " " Descriptions of New Species of Fossils, etc., p. 49. 1861. 



H Rep. N. Y. State Cab. Nat. Hist., p. 77. 1862 



" " " Illustrations of Devonian Fossils: Cephalopoda. Explanation of pi. 38. 1876. 



Shell straight, regularly enlarging from the apex to near the aperture. Trans- 

 verse section circular. Apical angle varying, in normal and compressed 

 specimens, from six to nearly eight degrees. Initial extremity observed, 

 but the characters are obscure. 



Chamber of habitation well developed, having a length equal to about 

 three times its diameter at the last septum, regularly expanding to a point 

 near the aperture where it is slightly contracted. Air-chambers numerous, 

 increasing in depth from the apex to the outer chamber, where the depth is 

 about three mm. 



