﻿1G GANOID FISHES OF THE CARBONIFEROUS FORMATION. 



which may be called post-frontal, though it is indeed placed rather forward, and cannot 

 be supposed exactly to represent the bone usually called " post-frontal " in osseous fishes 

 (Sphenotic, Parker), which is an ossification in the periotic cartilage. It seems, however, 

 to be the equivalent of the small superficial plate seen external to the posterior part of 

 the outer margin of the frontal in Amia, and which, in that fish, coexists with a subja- 

 cent well-developed " sphenotic ;" a corresponding ossification external to the frontal may 

 also be traced in the cranial buckler of Acipenser. In advance of the two frontals, and 

 forming the prominence of the snout projecting over the mouth, is a large median super- 

 ethmoidal (e.) ; its right and left lateral margins are notched anteriorly, and just above the 

 mouth, for the nasal openings (n.), one on each side. This lateral margin of the super- 

 ethmoidal articulates also on each side with another bone (a./.), which forms the anterior 

 part of the orbital margin of the cranial shield in front of the post-frontal and completes 

 the nasal notch of the first-named bone into a round opening. This we may call pre- 

 frontal, pretty sure, however, that it has nothing to do with the well-known ossification 

 in osseous fishes usually bearing that name, and which Mr. Parker has proposed more 

 definitely to term " ecto-ethmoidal." 1 



In all the other genera of Palceoniscidce, in which the cranial roof bones are well 

 enough preserved to admit of recognition, the same general arrangement seems to prevail 

 as in Nematoptychius. In Palcsoniscus (e. g. P. macropomus, PI. I, fig. 3), the very 

 same bones, bearing the same relations to each other, may be easily made out, with the 

 exception of the post-frontal, whose differentiation from the frontal is somewhat indistinct 

 in all the specimens I have seen. There, as in several other genera, the buckler is 

 proportionally wider in the parietal, narrower in the orbital and ethmoidal regions, than in 

 Nematoptychius. Only in Nematoptychius and Rhadinichthys have I distinctly seen the 

 nasal openings. 



That there were ossifications in the side walls of the primordial cartilaginous cranium 

 of the Palceoniscidcs is sufficiently evident from appearances presented by a few specimens 

 Elonichthys, Rhadinichthys), but in no case are those appearances of sufficient distinctness 

 to admit of description; but in a specimen of Gonatodus punctatus, from Wardie, a lucky 

 fracture has disclosed a beautifully developed parasphenoid {pa. s.) represented in PI. II, 

 fig. 5. This bone is rather short and broad, its centre of ossification is placed a little 

 in front of its posterior third, and opposite this there is on each side a slight constriction. 

 The part in front of the ossific centre is slightly excavated or furrowed longitudinally 

 when seen from below, the shorter and broader part behind being almost entirely 

 occupied by a gently convex triangular area with anteriorly directed apex, on each side of 

 which is a small flattened triangular wing. The " sphenoideum " represented by Dr. 

 Martin, in Palcsoniscus (op. cit., pi. xxii, fig. 8), is nothing more than a portion of the 

 palatal arch seen from above. 



Dr. Martin has also, in a crushed and badly preserved head of Palcsoniscus Freiesle- 

 1 "On tbe Structure and Development of the Skull in the Salmon (Salmo Salar, L.)," 'Phil. Trans.,' 1872. 



