﻿160 LEIDY'S DESCRIPTIONS OF REMAINS OF FISHES FROM 



Dendrodus of the Old Red Sandstone,* in which the superior maxillae are segmented, 

 therefore it is a fair inference that the fossil in question is a portion of an upper jaw. 



The maxillary segments of the fossil are beveled off on each side anteriorly to a 

 nearly acute edge, and are excavated posteriorly, so that the succeeding segments shall 

 lit into those in advance. Each segment contributes to the sides of the jaw a band- 

 like surface curving from the dental border as far back as the position of the second 

 succeeding tooth, and then turning forward at a nearly right angle to the base of the 

 jaw, so that when the segments are conjoined they appear separated on each side 

 by >» like grooves. 



Near the middle of the anterior margin of the beveled portion of the segments, on 

 both sides there exists an oval foramen, the apparent continuation of a dental canal. 



The teeth of the fossil are so closely set upon the jaw that the anterior basal angle 

 of those behind passes the contiguous angle of those in advance. Of the portions of 

 four teeth retained in the fossil, two are sufficiently well preserved to obtain some idea 

 of their form when perfect, as represented in the outlines of figure 1, plate 15. In general 

 form they appear to be like those of Charcharodon, but differ in a number of impor- 

 tant characters. They are compressed, conical, with coarsely dentated, trenchant 

 edges. Their two broad sides are symmetrical ; and they curve forward, so that in 

 the restored condition their anterior margin appears to be convex and the posterior 

 margin concave. Their base presents on each side a lobe-like expansion which ex- 

 tends upon the sides of the jaw, so that they look as if they were excavated and fitted 

 upon the dental border of the maxillary segments. 



The width of the teeth at base is one inch and nine tenths, the thickness in the 

 same position four fifths of an inch, and the probable length is about two inches. 

 The denticles are slightly compressed conical, with trenchant edges, and are nearly 

 two lines long and over one line broad. In structure the teeth are solid and consist 

 of hard dentine, which is however of looser texture toward the centre ; and they 

 are invested with smooth, shining enamel, about the one sixth of a line in thickness. 



The teeth arr firmly coossified with the maxillary segments, and indeed their 

 dentinal structure is absolutely continuous with, and undistinguishable by the naked 

 eye from the nearly equally dense ossific structure of the jaw. 



A careless inspection of the fossil, at its posterior broken border would mislead one 

 to suppose the teeth were inserted by long fangs into the jaw, an appearance which 

 arises from the narrow portion of one fragment, continuous with its tooth, being 

 received into the excavation of the segment in advance. 



Plate 15, figs. 1, 2. — Views of the two broad surfaces of a fragment of the jaw of Edestus vorax. 

 fig. 3. — Outline view of a vertical section of the jaw. 

 fig. 4. — Outline of transverse section of the teeth, from the same specimen. 



* Agaesiz, Pois. Foss. t. ii, pt, 2, p. 13. 



