﻿THE CARBONIFEROUS AND DEVONIAN FORMATIONS. 161 



ORACANTHUS, Agassiz. 



Oeneric Characters. Dorsal rays very large, compressed conical, with a large interior 

 cavity ; the external surface furnished with oblique and longitudinal rows of tubercles 

 or tuberculated ridges ; without posterior rows of denticles. 



Oracanthus vetustus, Leidy. 



Proc. Acad. Nat. Sci., vii. 414. This species is proposed upon an ichthyodorulite 

 or dorsal ray, from the collection of Mr. Timothy Conrad, now forming part of the 

 cabinet of the Academy. The specimen is from Missouri Territory, but the exact 

 locality from which it was obtained is unknown. It is dense, jet black, and heavy ; 

 and it has its apex and base broken away. On one side towards the base it is crushed 

 inwardly, and in this position there is a portion of adherent iron gray limestone, with 

 a partially imbedded segment of a crinoidal stem, which Mr. Conrad views as an evi- 

 dence that the dorsal ray was derived from the carboniferous limestone. In several 

 places the ray is fissured ; but the parts appear to have retained their original relation- 

 ship, and the form of the ray is nearly perfect. 



In its present condition the specimen is five inches long and two and two-thirds of 

 an inch wide at the base ; and its thickest portion is about eight lines. Its form is 

 flattened pyramidal and is curved a little backward and slightly also to one side. The 

 broad sides and posterior margin are thickly covered with mammillary tubercles but 

 the anterior margin is smooth. Between the tubercles the surface is slightly striated. 

 On the right side the tubercles are arranged in rows, irregularly longitudinal, and 

 irregularly oblique in the transverse direction. On the left side they are arranged 

 more regularly in longitudinal rows, and they evince a tendency to become confluent 

 in short transverse rows, which pursue an irregular waving course across the ray. 

 On the posterior margin, which is obtuse, there are several longitudinal rows. The 

 anterior margin of the ray is more obtuse than the posterior ; and it narrows 

 towards the base. The thickness of the walls of this ichthyodorulite is not easy 

 to ascertain. The apex of the specimen exhibits a solid bony structure, but the base 

 appears to present thin lateral walls and a thick wall to the anterior border. 

 Plate 16, figs. 1, 2, 3. — Different views of the ichthyodorulite of Oracanthus vetustus. 



PETALODUS, Owen. 



Generic Characters. Teeth with fangs. Crown demi-compressed-pyramidal, broader 

 than long, with trenchant margins, surrounded by a basal cingulum composed of 

 narrow imbricating folds, and descending lower on one side than the other. Fang 

 large, undivided, laminar. 



Petalodus alleghaniensis, Leidy. 



Sicarius extinctus, Leidy, Proc. Acad. Nat. Sci., vii, 414. 



This species of Petalodus is established upon the specimen of a tooth, which Mr. 



