﻿INTRODUCTION. 



7 



described as Ganoids by Agassiz have been by subsequent writers confidently referred to 

 the Teleostei, their true position still awaiting further investigation. 



This undoubted passage towards the Teleostei seems to be the principal reason that 

 of late years more than one author has been led to question the desirability of retaining 

 the Ganoidei as one of the great divisions of Fishes, notwithstanding that Agassiz 

 considered the establishment of this Order as his own greatest achievement in ichthyology. 

 Cope, for instance, has retained as an order only the Crossopterygii ; the Acipenseroid, 

 Lepidosteoid, and Amioid forms being united with ordinary osseous fishes in his order 

 of " Actinopteri." 1 Thiolliere had previously, in classifying the fishes of the Jura, 

 proposed to revert to the system of Cuvier, except as regards the Sturgeons, which along 

 with the other Agassizian Ganoids he placed in the division Malacopterygii abdominales 

 of the Pisces Ossei. 2 In like manner Liitken has proposed to include, not merely the 

 entire series of Ganoids, but also the Dipnoi, in the Physostomous division of Midler's 

 Teleostei? 



A careful perusal of Dr. Liitken's elaborate memoir has, however, failed to convince 

 me of the advantage of his position. The recent researches of Professor Huxley into the 

 anatomy of Ceratodus 4, go to show that the Dipnoi, notwithstanding their Ganoid 

 affinities, are better retained as a distinct order ; much less, then, can a position be claimed 

 for them among the Teleostei. For the rest, it does not seem to me that the occurrence 

 of transitional forms destroys the validity or naturalness of an " order " if its members 

 otherwise form a well-connected series, such as the Ganoids seem to do, if we meanwhile 

 leave out of view the problematic groups of Acanthodei, Placodermi, and CepJialaspida, 

 which must still be considered as " incertm sedis." We cannot doubt that the strict 

 separation of groups which, however natural they may be, must always be more or less 

 arbitrary, and that were we really acquainted with the entire succession of organic forms 

 such things as absolutely defined " orders," &c, would be found to have no existence in 

 nature. And lastly, it must be borne in mind that the relative value of certain 

 structural characters as being of "ordinal," " subordinal,'' or "family" importance, 

 frequently very much depends upon the subjective idiosyncrasy of the writer. 



The arrangement of the Ganoids in minor subdivisions is, in the present state of 



1 "Observations on the Systematic Relations of the Fishes" (abstract), 'Ann. and Mag. Nat. Hist.' 

 (4), ix, 1872, pp. 155—168. 



2 "Note sur les Poissons fossiles du Bugey, et sur 1' Application de la Metbode de Cuvier a leur 

 Classement," 'Bull. Soc. Geol. de France,' 1858. (Reprinted in the second part of the "Poissons 

 Fossiles du Bugey," Paris and Lyons, 1873, pp. 8 — 11). 



3 " Ueber die Begrenzung und Eintheilung der Ganoiden," von Dr. Cbr. Liitken, aus detn Danischen 

 iibersetzt von Dr. R. v. Willemoes-Suhm, ' Paheontographica,' Bd. xxii, lste Lieferung, 1873. The 

 original essay is contained in the ' Videnskabelige Meddelelser fra den Naturhistoriske Forening 

 i Kjobenhavn," 1868. 



* "Contributions to Morphology. Ichthyopsida — No. 1. Ceratodus Forsteri, with observations on 

 the Classification of Fishes," ' Proc. Zool. Soc.,' January, 1876. 



