40 Fossil Fishes. 



of the true position of this class in the scale of living beings. Pla- 

 ced higher than the radiata and the mollusca, they present peculiar- 

 ities of organization more numerous, and also subject to greater dif- 

 ferences ; and in them also we remark, within narrower geological 

 limits, more marked differences than among animals lower in the 

 scale. In the class of fishes, we do not see genera, nor even fami- 

 lies, run throughout a whole series of formations with species which 

 often differ but very little in appearance, as happens in the Zoo- 

 phytes ; on the contrary, this class, from one formation to another, 

 is successively represented by very distinct genera, referable to fam- 

 ilies which themselves soon vanish, as if the complicated apparatus 

 of a superior organization could not be long perpetuated without inti- 

 mate modifications ; or rather, as if animal life had a more rapid ten- 

 dency to change in the higher orders of the animal kingdom, than in 

 those lower in the scale. In this respect, it is with fish nearly as it 

 is with the mammifera and reptiles, whose species, in general very 

 limited, belong in the series of formations with little verticla distance, 

 to genera which are different, without passing insensibly from one for- 

 mation to another, as is often witnessed in certain shells. This is 

 one of the most interesting facts which I have observed, namely, 

 that I do not know a single species of fossil fish which is successive- 

 ly found in two formations, whilst I know a great number which have 

 a considerable horizontal distribution. Besides, the class of fishes 

 moreover presents to zoological geology the immense advantage of 

 extending across all the formations, and of presenting in a class of 

 vertebral animals a point of comparison regarding the differences 

 which exhibit themselves in the longest lapse of known time, of ani- 

 mals constructed generally on the same plan — of animals of a class 

 which already counts a very great number of fossil species, for the 

 most part referable to types which exist no longer ; and whose af- 

 finities with the living species are as distinctly marked as those which 

 ally the Crinoidea to the ordinary Echinodermata, the Nautili, and 

 the Sepia to the Belemnites, and the Ammonites, the Pterodactyli, 

 the Ichthyosauri, and the Plesiosauri to our Saurians ; and the liv- 

 ing Pachydermata to those which of old, inhabited the borders of 

 the lakes around Paris, or the planes of Siberia. 



" The fishes of the tertiary rocks, are those on which I the least 

 dilate, because they approach nearest to the living species, and be- 

 cause their study may be undertaken by means of works which are 

 already published upon Ichthyology. At the same time, consider- 



