28 
PALEONTOLOGY OF NEW YORK. 
Orthoceeas Dagon. 
PLATE CXXIX, FIG. 1. 
Orthoceras Dagon, Hall. Fifth Ann. Kept. State Geologist. Expl. pi. (129) 14, fig. 1. 1886. 
This species is represented by a large septate fragment, preserving the 
base of the chamber of habitation with about tivo-thirds of the air-chambers 
attached. The entire length of the fragment is 223 mm. Although based on 
imperfect material, the distinguishing characters are so pronounced as to readily 
distinguish the species from any other form previously indicated from the same 
horizon. 
The principal features are ; The rapid enlargement of the tube, with the con¬ 
sequent large apical angle ; and the broad retral curvature of the septal sutures 
on what is probably the ventral side. 
Distribution. In the Upper Helderberg limestone, Columbus, Ohio. 
Orthoceras rudens. 
PLATE CXVlII, FIG. I. 
Orthoceras rudens. Hall. Fifth Ann. Kept. State Geologist Expl. xfi- (118) 2, fig. 1. 1886. 
The species is represented in the collections by a compressed fragment of the 
chamber of habitation, having a length of a little more than 100 mm. The 
tube is marked by longitudinal striae and ornamented by numerous regular 
annulations, of which there are three in the space of 10 mm., showing a well- 
defined retral curve on the ventral side. 
This form differs conspicuously from 0. crotalum (Pal. N. Y., vol. v, pt. 2, p. 
296), and 0. codamm {id., p. 298), in its larger size and comparatively more 
frequent and depressed annulations. The surface characters more nearly 
approach those of 0. nuntium {id., p. 299), but the annulations are broader, less 
abrupt, and the strong retral curve in the ornamentation on the ventral side 
are not present in that species. 
Distribution. The type specimen is from an argillaceous limestone, and is 
recorded as from the Hamilton group, in Livingston county. 
