﻿Miss Agnes Crane — On Certain Living and Fossil Fishes. 217 



Ctalk, and the Polypterini, comprising only the living Pohjpterns and 

 Calamoichthys of Africa, alone represent this once prevailing race of 

 fishes at the present day. The genus Folypterus is remarkable for 

 the unique arrangement of its sub-divided dorsal fin, and by the 

 possession of a double cellular air bladder, which most nearly approxi- 

 mates to the lungs of the Dipnoi. It has least structural affinities 

 with the Coelacanths, its nearest allies in time, and is most closely 

 zoologically related to the rhomboidal scaled Saurodipterines of the 

 Devonian, from which it is separated by an enormous gulf of geolo- 

 gical time, as no intermediate links have been discovered. 



In the notochordal Phaneropleurini we find forms which most 

 closel}' resemble the acutely lobate finned Lepidosiren. The shape 

 of the body, number, position, and structure of the fins, and all the 

 elements of the internal skeleton, exactly foreshadow those of the 

 mud-fishes. Like them Phaneropleuron was covered with thin 

 cycloidal scales, through which the long and well-ossified ribs show so 

 plainly in the fossil state as to suggest the name of the genus. The 

 dentition, however, differs from that of Ceratodus and Lepidosiren, 

 being composed of a row of short conical teeth in each jaw ; and in 

 the absence of the grooved dental plates so characteristic of the true 

 dipnoi, it is uncertain whether this family can be associated with the 

 other members of that order. The chain of descent is carried on by 

 the Coelacanthini, the only fringe-finned ganoids occurring in the 

 Mesozoic rocks. They can be traced up from Coelacanthus in the 

 Carboniferous, through Holophagus in the Lias and Undina in the 

 Oolites, up to Macropoma in the Chalk. The family is distinguished 

 by cycloid scales, hollow fin supports, and a notochordal skeleton 

 built on the same principle as that of the mud-fishes. In some 

 genera the walls of the air bladder are ossified. This peculiarity, 

 which was first suspected by Mantell, is especially remarkable in 

 Undina and Macropoma. No fossil Crossopterygids have been dis- 

 covered in Tertiary strata, but it is the opinion of Professor Huxley 

 that, as the rhomboidal scaled Saurodipterines of the Devonian rocks 

 are now represented by the living Folypterus, so the stifle-walled 

 lungs of the Lepidosiren are the homologues of the ossified air 

 bladder of the Coelacanths, and thus that genus carried up the 

 cycloidal branch of the Crossopterygids to the present day. 



Such, in the abstract, is the life history of fishes, a class character- 

 ized, like other divisions of the animal kingdom, by the extincti(.)n of 

 some groups after a brief existence, and by the persistent endurance 

 of others through untold ages. In the few genera of living ganoids 

 we have undoubtedly the surviving descendants of a numerous and 

 powerful race which prevailed in the Devonian epoch, and by the 

 discovery of fossil dipnoal forms the progenitors of Ceratodus and 

 Lepidosiren, the Dipnoi are likewise proved to be of ancient lineage. 

 The greater part of the existing piscine fauna, on the contrary, is 

 shown to be of comparatively modern date. Moreover, in con- 

 sidering the fact that the early fishes are remarkable from a combi- 

 nation of diverse characteristics which subsequently become the dis- 

 tinguishing peculiarities of distinct families, and of a higher order, 



