﻿164 LEIDY'S DESCRIPTIONS OF REMAINS OF FISHES FROM 



A bone, the most perfect specimen preserved of the remains of Holoptychius ameri- 

 canus, represented in figure 4, plate 17, appears to be one of the branchiostegal plates. 

 Itis trilateral, is sixteen lines wide, and appears to have been about twenty-two lines long. 

 Its surface exhibits numerous short flexuose ridges, and tubercles, characteristic of the 

 cranial bones of the genus. 



Plate 16, figs. 9, 10. — Scales of Holoptychius americanus. 

 Plate 17, fig. 1. — Tooth of H. americanus. 



fig. 2. — Transverse section of the same tooth. 



fig. 3. — Fragment of the lower jaw 



fig. 4. — A branchiostegal plate. 



STENACANTHUS, Leidy. 



Generic Characters. Dorsal spine long, narrow, straight, compressed conical, hollow, 

 longitudinally striated, furnished posteriorly with marginal rows of oblique denticles. 



Stenacanthus nitidus, Leidy. 



Proc. Acad. Nat. Sci., viii, 11. This genus and species are indicated by the specimen 

 of an ichthyodorulite, imbedded in a fragment of rock of the Old Red Sandstone For- 

 mation of Tioga County, Pennsylvania, and discovered by Charles E. Smith, Esq., who 

 presented it to the Academy of Natural Sciences. In the same fragment of rock with 

 the spine, there are also small portions of bones, and the impression of a tooth, 

 apparently of Holoptychius. 



The specimen has its apex broken off, and also a portion of its left wall, exposing a 

 large interior cavity, filled with the sandstone matrix. ^ It appears to have been per- 

 fectly straight in its length, and is long, narrow, compressed conical. The anterior 

 border is convex : the sides are longitudinally striated or grooved ; and the posterior 

 border is denticulated. There appears to be a pair of close rows of denticles, though 

 the specimen only exhibits one. The denticles are triangular, directed obliquely down- 

 ward and backward, and seven of them are equal to the space of half an inch. 



About half an inch below the broken summit of the specimen, a zigzag fissure or 

 perhaps a suture crosses the spine, as represented in figure 7 of plate 16. From the 

 two lower angles of the fissure, two others proceed longitudinally downward to the 

 broken margin of the specimen. These appear like real sutures, though they are most 

 probably mere cracks, the result of fracture. 



The length of the ichthyodorulite in its present condition is two inches and two 



thirds, and its width at base about half an inch. 



Plate 16, figs. 7, 8. — Ichthyodorulite of Stenacanthus nitidus ; the former figure representing merely the 

 outline. 



APEDODUS, Leidy. 

 Generic Characters. Opercular bones, thick, covered with hard and finely granulated 

 enamel. Teeth large, compressed conical, with trenchant margins and a grooved base. 



