28 PALEONTOLOGY OF NEW YORK. 



Orthoceras Dagon. 



PLATE (XXIX, FIG. 1. 

 'Jtoceras Dagon, Hall. Fifth Ann. Rept. State Geologist. Expl. pi. (129) 14, fig. 1. 1S86. 



Tins species is represented by a large septate fragment, preserving the 

 base of the chamber of habitation with about two-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 CXVIII, FIG. I. 

 Orthoceras widens, Hall. Fifth Ann. Rept. State Geologist Expl. pi. (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- 

 deli ned retral curve on the ventral side. 



This form differs conspicuously from 0. crotahm (Pal. N. Y., vol. v, pt. 2, p. 

 296), and 0. calamen (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. 



