164 GANOID FISHES OF THE CARBONIFEROUS FORMATION. 



of the caudal fin. It yields us in the first place a view of the external markings of the 

 scales and of the fin-rays. The scales resemble those of the Jermyn Street specimen in 

 size and in form, the ornament which is seen on their outer surfaces (tig. 2) consisting 

 of fine flexuous ridges passing into tubercles and mainly horizontal in direction. The 

 pectoral fin has, as in the other specimen, a broad rounded contour, but its termination 

 extends as far as to opposite the commeneement of the ventral, the contour of which is 

 well preserved and shows some minute fulcra along the anterior margin ; the dorsal fin 

 commences opposite the origin of the ventrals ; the anal fin is of the usual triangular 

 acuminate form; the tail-pedicle seems unusually deep for the size of the fish; the 

 sculpture of the joints of the fin-rays consists of fine longitudinal striations (fig. 3). 



The British Museum specimen, as it lies on the stone before us, differs obviously 

 from the Jermyn Street one in the following particulars : 



(1) The fins on the ventral aspect of the body and the intervals between them are 

 smaller. For example the pectoral fin, as has been already remarked, has its apex reach- 

 ing to opposite the commencement of the ventral. 



(2) The dorsal fin is situated further forwards, the front of it being opposite the 

 beginning of the ventral. 



(3) The caudal pedicle is proportionately deeper than in the Jermyn Street speci- 

 men, at least it is so calculating from the contour of the hinder extremity of the body 

 in that specimen. 



Now, of these discrepancies, only two explanations are possible — either we are dealing 

 with a distinct species, or the British Museum specimen has been, as is so common 

 with the Palaeozoic " Ganoids," subjected to deformation by irregular pressure during 

 the process of fossilisation. The latter explanation seems to me to be the more readily 

 acceptable, and Dr. Smith Woodward has already in his description of the specimen in 

 question noticed " the crushing of the head a little downwards and backwards upon the 

 anterior part of the abdominal region." I would refer the apparent anterior position of 

 the dorsal fin and the appearance of the tail-pedicle to the same cause. 



Geological Position and Locality. — From the Coal Measures (Upper Carboniferous) of 

 Co. Kilkenny, Ireland. 



Genus — Phanerostkon, Traquair, 1881. 



Generic Characters. — Fusiform; completely heterocercal ; dorsal fin acuminate, but 

 not, strictly speaking, triangular ; anal fin commencing opposite the middle of the 

 dorsal; caudal inequilobate, bifurcated; rays of all the fins delicate, bifurcating once; 

 fulcra absent ; principal rays of pectoral articulated. Head typically Palaeoniscoid in 

 structure, with oblique suspensorium, and anteriorly-placed orbit ; maxillary and 

 mandibular teeth conical, sharp, enamel-capped, and of different sizes, the smaller ones 



