34)1 PALEONTOLOGY OF NEW-YORK. 



CEPHALOrODA. 



The fossils of this class are comparatively rare in the Lower Helderberg 

 group, and the condition of the specimens is generally such as to render 

 the determination of species quite unsatisfactory. A single species of 

 Oncoceras, one of Cyrtocebas, and a few species of Orthoceras, constitute 

 all that we know at the present time. 



While in this period the Gasteropoda acquire a development unknown 

 in any other geological period of our country, the development of the 

 Cephalopoda appears almost at the minimum degree, presenting less 

 variety of form than in the preceding and following geological periods. 

 It is not improbable, however, that some localities may yet furnish a 

 greater number of species and a greater variety of forms. 



Oncoceras oToides ( n. s.). 



Plate LXIX. Fig. 2 a, h. 



Shell ovoid, slightly arcuate below the apex, expanding, ventricose ; 



outer cavity large. Septa gently concave ; those near the apex distant 



from each other less than one-eighth of an inch, the distance increasing 



in the outer divisions : several of the later septa, adjacent to the outer 



cavity, crowded closely together. Surface unknown. 



The only specimen which I have seen is a cast; the apex is removed, and other- 

 wise imperfect. 



Fig. 2 a. A longitudinal section of the Bpecimen, showing the crowded septa near the outer 

 chamber. 



Fig. 2 h. The exterior of the oast of the same specimen. 



Geological position and locality. In the upper part of the tentaculite limestone : 



Herkimer county. 



Cyrtoceras subrectum ( h. s.). 



Plate LXIX. Fio. 3 a, b, c, d. 

 Shell terete, gradually tapering, very gently curving ; section scarcely 



