CEPHALOPODA 



DESCRIPTIONS OF SPECIES. 



Note. — The following descriptions and accompanying plates are supplementary to the fossil cephalopoda 

 presented in Volume V, part II. of the Palaeontology of New York. After the completion of that volume, 

 there still remained in the possession of the author, some new or undescribed material, and a number of 

 specimens which were important as illustrating additional features of some of the previously established 

 forms. The descriptions of a number of the species presented on the supplementary plates, were prepared 



in time to be included in their proper place in the volume. Such species are here rely cited, and referred 



to volume v, part 2. It has been necessary to restrict the length of the descriptions here given, on account 

 of the contract limitations for the present volume. 



At the close of Volume V, part ii, in 1879, the Cephalopoda were com- 

 mitted to the charge of Mr. C. E. Beecher, who has furnished the following 

 descriptions : 



ORTHOCERAS, Breynius. 1732. 



Orthoceras duramen. 



PLATE (JXVII, FIG. 1. 

 Orthoceras duramen. Hall. Fifth Ann. Kept. State Geologist. Expl. pi. (117) 1, fijj. 1. lSSti. 



Shell straight, robust, rapidly enlarging to the chamber of habitation. Apical 

 angle ten degrees. The specimen described is a compressed septate frag- 

 ment, and the true form of the transverse section cannot be ascertained. 

 Initial extremity unknown. 



Air-chambers 15 to 20 mm. in depth. 



Septa thin, deeply concave. Sutures straight, marked on the internal 

 mould by narrow depressed zones, as in 0. cingulum (Pal. N. Y., vol. v, pt. 2, 

 p. 240). 



Siph uncle and test not observed. 



