Affinities of the Genus Pleuracanthus. 357 



it can no longer be justifiable to rank it among the Ganoids 

 ' sans phrase] but that even those who will not allow it to be a 

 Teleostean must attach to it the warning adjunct of incertce 

 sedis." And further, " Why should not a few Teleosteans 

 have represented their order among the predominant Ganoids 

 of the Devonian epoch, just as a few Ganoids remain among 

 the predominant Teleosteans of the present day ? When it 

 is considered that an ichthyologist might be acquainted with 

 every freshwater and marine fish of Europe, Asia, South 

 Africa, South America, the Indian Archipelago, Polynesia, 

 and Australia, and yet know of only one Ganoid, the stur- 

 geon (a fish so unlike the majority of its congeners that a 

 naturalist might be well acquainted with almost all the 

 fossil Ganoids and yet not recognize a sturgeon as a member 

 of the group), it will not seem difficult to admit the existence 

 of a Teleostean among the Devonian Ganoids, even though 

 that Teleostean should in some, even important, points differ 

 from those with which we are familiar." 



The relationship of the peculiar fishes of the Old Red Sand- 

 stone to the Siluroids of the present time, so clearly enun- 

 ciated by Prof. Huxley, and, so far as can be defined with our 

 present limited knowledge, with every appearance of proba- 

 bility and truth, carries back the advent of Teleostean fishes 

 to the earliest geological periods during which fishes are known 

 to have existed. Along with the Ganoids they have the 

 greatest claim to antiquity of all the fishes whose remains 

 have been identified. It is possible that the two groups may 

 have had much in common, and that a common ancestry in 

 some intermediate form may be discovered in still older rocks. 

 In the fishes from the Coal-measures, which form the subject 

 of this communication, there seems to be something very like 

 a bridge, a transitional form between the then predominant 

 Elasmobranchs and the Siluroid Teleosteans. Its affinities 

 appear to be decidedly on the side of the Siluroids ; and it may 

 best be considered as a forerunner of that great group of fishes. 

 In geological time Pleuracanthus is known to extend from the 

 Lower Coal-measures, through the Middle and Upper Coal- 

 measures, of England and America, occurring in the gas- 

 coals of Bohemia (regarded as intermediate or passage-beds 

 between the Carboniferous and Permian rocks), and up into 

 marl slates of the latter group. It remains to be seen what 

 were the successive steps in development which have resulted 

 in the completely ossified and highly organized Siluroids now 

 existing. 



