﻿18 GANOID FISHES OF THE CARBONIFEROUS FORMATION. 



seems to be composed of an elongated bony plate, evidently a membrane ossification covering 

 the inner or oral aspect of a palatal cartilage like that of Polyodon, in which a very similarly 

 shaped membrane bone also exists (PI. VII, figs. 1 and '2, pa.). It is probably equivalent 

 to the ectopterygoid of osseous fishes. Posteriorly, however, there is apparently another 

 and much smaller bony piece {q.) close to the articulation of the jaw, and which Ave may 

 pretty safely assume to be a true quadrate ; above which there is, in Nematoptychius and 

 Elonichthys, at least, distinct evidence of a third piece occupying much the same position 

 as the metapterygoid in ordinary fishes. 



Placed externally to the palato-quadrate lamina is the very peculiarly shaped maxilla 

 (PI. I, fig. 2 and 11, mx.). This is broad behind, where it covers a large part of the cheek, 

 but just behind the orbit its upper margin is suddenly excavated or cut away, so that its 

 anterior extremity becomes attenuated to a fine point as it passes on below the orbit to 

 the premaxillary region. Behind the orbit the upper margin of the maxilla is horizontal 

 and straight, and joins the somewhat oblique posterior one at an obtuse angle ; the 

 posterior-inferior angle, slightly rounded, overlaps the lower jaw a little at its articulation. 

 The lower or dental margin is slightly sigmoidal in its contour, passing first forwards and 

 a little upwards, then horizontally forwards, and finally near its anterior termination a 

 little upwards again. Excepting posteriorly, where it overlaps the mandible, the lower 

 margin of the maxilla is slightly reflected inwards so as to form a sort of narrow ledge, 

 which, apparently, came in contact with the infero-external margin of the palatal lamina. 

 There does not, however, seem to have been here any such firm articulation by suture as 

 we find in Polypterus. 



Owing to its small size and the manner in which the heads are crushed, it is extremely 

 difficult to make out the premaxilla in Palceoniscus and most of the other genera. It is, 

 however, very clearly exhibited in that specimen of Nematoptychius which has already 

 served as a basis for the description of the bones of the cranial roof. It is a small bone 

 {p. mx., PL I, fig. 8) placed at the anterior inferior corner of the orbit, meeting with its 

 fellow of the opposite side below the projecting super-ethmoidal, with which bone, and 

 with the prefrontal, it is firmly and immovably articulated by suture. It bears teeth like 

 those of the maxilla. The small piece of bone marked p. mx. in the figure of the head 

 of Palceoniscus macropomus, PI. I, fig. 3, is, in all probability, the premaxilla a little 

 displaced by crushing. 



The mandible, owing to the great backward extent of the gape, is long, and in some 

 cases rather slender, as in Palceoniscus and Amblypterus, though in many, especially in the 

 more predaceous forms, such as Pyyopterus, Acrolepis, Nematoptychius, it is sufficiently 

 stout. In all it is of a tapering form ; in some {Palceoniscus) it is tolerably straight when 

 seen laterally, in others {Nematoptychius) the side view shows a gentle curvature with 

 upwardly directed concavity. The Meckelian cartilage was evidently largely persistent, and, 

 at least, four osseous elements can be distinctly made out. Of these the dentary bone 

 (PI. I, fig. 2, &c, d.) is, of course, the most conspicuous, and extends nearly the whole 



