CLASSIFICATION OF DEVONIAN FISHES. 



25 



This is the family of the Phaneropleurint, which I have esta- 

 blished to contain the singular genus Pltaneropleuron, described at 

 length in this Decade (p. 47) and figured in Plate III. The general 

 character of this fish, its thin cycloid scales, the mode of termi- 

 nation of its caudal extremity, and its remarkable, very acutely 

 lobate, ventral fins, lead me to entertain very little doubt that its 

 right place is among the Crossopterygidse, and in the neighbonr^ 

 hood of the Glyptodipterini and Ccjelacantliini, though I have not 

 yet been able to obtain a very good view of its jugular plates. But 

 the very long, single, dorsal fin, the great length and acute lobation 

 of the ventral fins, which seem to have been longer than the pectorals, 

 and the complete ossification of the costal elements and neural arches 

 throughout the vertebral column, separate Phaneropleuron alike 

 from the Glyptodipterini and the Coelacanthini. From the Cteno- 

 dodipterini it is separated not only by these characters, but by its 

 dentition. Under these circumstances the only course seems to be 

 to regard it as the type of a distinct family. 



The group of Crossopterygidse, as thus established, appears to 

 me to have many remarkable and interesting zoological and 

 palseontological relations. Of the six families which compose it four 

 are not only Palseozoic, but are, some exclusively and all chiefly, 

 confined to rocks of Devonian age, — an epoch in which, so far as 

 our present knowledge goes, no fish belonging to the suborders 

 of the Amiadse or Lepidosteidse (unless Cheirolepis be one of the 

 latter) makes its appearance. Rapidly diminishing in number, the 

 Crossopterygidse seem to have had several representatives during 

 the Carboniferous epoch, but after this period (unless Ceratodus be a 

 Ctenododipterine) they are continued through the Mesozoic age only 

 by a thin, though continuous, line of Coelacanthini, and terminate, at 

 the present day, in the two or three known species of the single 

 genus Polypterus. Polypterus, however, is clearly related to the 

 rhombiferous Crossopterygians, or in other words, to exactly that 

 group of whose existence we have no knowledge in any Mesozoic, or 

 Tertiary, formation ; while the Ctenododipterini and Coelacanthini, 

 which depart most widely from Polypterus, are those which con- 

 tinue the line of the Crossopterygidse from the Palaeozoic to the 

 end of the Mesozoic epoch. Thus both ends of the Crossopterygian 

 series appear, if I may use the expression, to be cut off" from the 

 modern representatives of the suborder ; Polypterus being separated 

 from those members of its suborder with which it has the closest 

 zoological relations, by a prodigious gulf of time, and from the 

 fossil allies which are nearest to it in time, by deficient zoological 



