342 
PALEONTOLOGY OF NEW-YORK. 
CEPHALOPODA. 
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 Cyrtoceras, 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 ovoides (n. s.). 
Plate LXIX. Fig. 2 a, b. 
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 specimen, showing the crowded septa near the outer 
chamber. 
Fig. 2 b. The exterior of the cast of the Same specimen. 
Geological position and locality. In the upper part of the tentaculite limestone : 
Herkimer county. 
Cyrtoceras subrectum (n.s ). 
Plate LXIX. Fig. 3 a, b, c, d. 
Shell terete, gradually tapering, very gently curving; section scarcely 
