﻿22 GANOID FISHES OF THE CARBONIFEROUS FORMATION. 



ossicles of the Acanthodidee ; of these the broadest and most conspicuous is that which 

 bounds the orbital opening below and behind, the others are extremely narrow and their 

 number excessively difficult to ascertain. But besides these there is in all Paleeoniscida 

 an outer, or rather posterior, set of suborbitals {s. o.), short, irregular, angular plates, 

 placed on the cheek in front of the prseoperculum and the broad part of the maxilla. In 

 Palceoniscus (PI. I, figs. 1 and 2) no fewer than five of these may readily be seen behind the 

 narrow circumorbital ring, and these seem to pass above that ring into a set of minute 

 quadrate ossicles between it and the external margin of the cranial buckler in that 

 region. So crushed, however, are all the heads of these fossils, and especially in 

 the region of the orbit, that the investigation of these bones is surrounded with extreme 

 difficulty. 1 



Branchial Apparatus. — Several specimens have occurred yielding evidence of very 

 complete ossification of the branchial skeleton. The best of these is represented in 

 PI. II, fig. 9 ; it is the bead of a small Monichthys from the limestone of South 

 Queensferry, crushed vertically, and seen from above. The cranium proper is gone, all 

 but its occipital portion, and in consequence a considerable amount of the branchial 

 skeleton is exposed, consisting of the median system of basibranchials from which 

 no less than three of the branchial arches, in the form of slender bony rods, may be seen 

 diverging outwards and backwards. The lines of separation between the probable 

 constituent osseous pieces of the portion of the branchial skeleton here exposed cannot 

 be distinctly made out. 



Fig. 8, PI. II, represents the head of a specimen of Elonichtlnjs Egertoni, in which 

 the branchial cavity is exposed in front of the shoulder-girdle, showing portions of three 

 of the branchial arches. In another specimen I have seen evidence of a fourth. 



1 Dr. Martin's representation of the circumorbital plates in his restored figure of the head of 

 Palceoniscus (op. cit., fig. a) is altogether erroneous, as is likewise the entire figure. 



His supposed discovery in Palceoniscus of "ossa intercalaria " similar to those of Polypterus is due 

 to a misinterpretation of the specimen figured by him (op. cit., fig. J). The original of this figure is a 

 cranial shield of P. Freieslebeni from Richelsdorf, in which the superethmoidal and anterior frontals are 

 deficient ; the frontals also are slightly mutilated at their anterior extremities. Sutures and divisions are 

 here indicated where none exist. His " occipitals" and " parietals" are both parts of the frontals, 

 the position of the real parietals, obscure enough in this specimen, being overlooked. The anterior of the 

 two so-called '■'intercalaria'" is the same portion of bone which he has elsewhere, as in figs. 2 and 3, 

 called " nasal," and which I have designated post-frontal in such cases as Nematoptychius, &c, where its 

 differentiation from the frontal is distinct ; the posterior one is part of the squamosal, the rest of the bone 

 being here marked " mastoid," while in fig. 3 the very same plate is in its entirety denominated 

 " temporal." 



