84 GANOID FISHES OF THE CARBONIFEROUS FORMATION. 



liyomandibulai- ; while the lower {y) is of a triangular shape, and fills up the gap 

 between the operculum, preopen-ulum, and subopei-culuni.^ The suboperculum {s.oj).) 

 is of the usual quachate form, and the preoperculuin has likewise the typical palaeaniscid 

 configuration, except that in accordance with the great length of the maxilla its upper 

 part is also rather longer than usual. The orbit is situated much in front, but none 

 of the specimens that I have seen give a clear view of the number and arrangement of 

 the circumorbital bones. 



The maxilla {mx.) is a conspicuous bone of the shape characteristic of the genus, 

 but its posterior broad part is rather longer than usual owing to the great extension 

 backwards of the gape. Tliis part of the l)one is shown in PI. XIII, fig. 3, the narrow 

 suborbital extension being here broken off; most of the bone has flaked away, leaving 

 behind merely an impression of the inner surface, but what remains shows the charac- 

 teristic tubercular ornament to be presently alluded to. Along the inferior margin are 

 seen numerous small sharp conical teeth, and also the proximal parts of some larger 

 ones, whose points are buried in the hard ironstone matrix. 



Covered by the maxilla externally is the palatoquadrate a])paratus, the aboral 

 surface of which forms a longitudinal groove curving downwards at its posterior 

 extremity, and which must have been occupied by the levator muscle of the lower jaw. 

 It is in this species of an unusually long and narrow form, and seems principally 

 composed of one large elongated palatoj)terygoid bone ; but though other elements are 

 also clearly present they cannot be defined. One remarkable thing is that between this 

 l)one and the anterior part of the maxilla there seems to have existed a narrow chain of 

 ossicles, four of which {x.) are seen in impression in the fragment represented in 

 PI. XIV, fig. 2, where pt. is the anterior part of the palatopterygoid bone (also 

 seen in impression), and d. the dentary of the mandible. I can, however, see no 

 <listinct evidence of sutures marking off these ossicles in other specimens of the bony 

 palate, in which the pieces in question are probably already fused by anchylosis witii each 

 other and with the adjoining palatopterygoid bone. These ossicles probably supported 

 laniary teeth like those similarly placed on ossicles along the outer edge of the palate in 

 the Rhizodont genus Eusthenopteron.^ 



PI. XIII, fig. 0, represents, natural size, a large mandible which measures four 

 and three quarter inches in length, and one inch in depth just behind the middle. 

 Most of the external bone has adhered to the counterpart, leaving an impression behind, 

 but some of the outer surface of the dentary element remains, showing the ornament of 

 contorted ridges already referred to. The bone of the angular element is gone, but the 

 articular is very distinctly seen, as is likewise the notch {ar.) for the articulation with the 



^ These two small plates, which are of common occurrence iu tl:e heads of Palaeoniscidae, are 

 represented in the figure of the facial bones of Elonichthys {Cosmoplychius) striatus (Pi. Ill, fig. 3), 

 the upper narrow one being left without name, while the lower one is designated " stcbopeycuJum.'^ 



2 E. H. Traquair, ' Geol. Mag.' (3), vol. x, 1893, p. 266. 



