CONTRIBUTIONS TO PALiEONTOLOGT. 73 



GENUS ORTHOCERAS ( Breyn). 



ORTHOCERAS PELOPS ( n. s.). 

 Shell robust, somewhat rapidly tapering : section circular ; si- 



phuncle central. 



This species is known to me only in the condition of casts of the 

 interior. Specimens are rarely found with a length of two feet, but 

 always imperfect. The outer chamber i^ very long and large. A 

 fragment of the septate portion seven inches long, the proportions of 

 which are pretty well preserved, has a diameter of two inches at 

 the larger and one inch at the smaller extremity. In a specimen 

 1*75 diameter at the larger end, three chambers measure 1'57 inches; 

 and in a specimen four inches long, with a diameter of one inch at 

 the smaller extremity, there are thirteen chambers. In a fragment 

 where the smaller extremity is less than half an inch, there are 

 twenty septa in a length of three and a quarter inches. 



There are some variations in the proportions between the parts, 

 and the number of septa in the same space, with an equal diameter. 

 The siphuncle is small; being scarcely more than three-twentieths 

 of an inch in diameter, and not more than half this diameter in 

 some of the smaller specimens. 



This is the common and abundant species of the Schoharie grit ; but it is 

 extremely difficult to find any but fragmentary specimens. 



Geological formation and locality. In the Schoharie grit at the Hel- 

 derberg mountains and Schoharie. 



ORTHOCERAS TETRICUM ( n. s.). 



In the more calcareous beds of the Schoharie grit, there is a 

 species of Orthoceras of a more gradually tapering form. The si- 

 phuncle is comparatively large and a little excentric : the septa, 

 where the diameter of the shell is an inch and a half, are half an 

 inch distant, or nine in the length of five inches and a half where 

 the diameter at the smaller end is one inch. The distance of the 

 septa is about double those of the preceding species, while it differs 

 from the 0. longicameratum of the Lower Helderberg group in the 

 lesser comparative distance of the septa. 



Geological formation and locality. In the calcareous part of the Scho- 

 harie grit : in the Helderberg mountains. 



1861.] 10 [Senate No. 116.] 



