64 



Hecherches sur les Poissons Fossiles. 



finding their remains in all formations, and the opportunity 

 they afford of comparing those differences which present 

 themselves throughout great lapses of time in animals con- 

 structed in general on the same plan, and belonging to a 

 single class of which we are already able to enumerate a 

 great number of fossils species, referable for the most part to 

 types which no longer exist, and whose affinities with living 

 species are equal to those which connect the Crinoides 

 to the ordinary Echnoderms, the Nautiles and the Sepia to 

 the Belemnites and to the Ammonites, the Pterodoc- 

 tyles, the Ichthyosaures and Plesidaures to our Sau- 

 rians, the living Pachydermata to those which inhabited 

 of old the borders of the lakes in the environs of Paris, or 

 the plains of Siberia. The fishes of the tertiary strata are 

 those on which I have dwelt least, because they approach 

 nearest to living fishes, and that their study falls rather 

 within the province of works, which we are already in pas- 

 session of on Ichthyology. Although we see enormous num- 

 bers of living fishes which they approach, it is found very 

 difficult in their state of preservation to identify them, or 

 rather to appreciate exactly their distinctive characters, to 

 which I have in general confined my observations. I have 

 not found one single species that could be satisfactorily iden- 

 tified with those of our seas, except one little species which 

 we found in clayey boulders in Greenland of an uncertain 

 geological age. 



The species of the Norfolk Craig, of the upper Sub-apennine 

 formation, and of the Molasse^ belong, for the most part, to 

 genera common in the tropical seas: such for instance as 

 the Platax, the large Carcharias,* the Myliobates with large 

 chevrons^ etc. 



In the inferior tertiary formation, in the London clay, in 

 the Calcaire grossier of Paris, and at Monte-Bolca, already 

 a third or more of the species are found to belong to genera 



* White Sharks, 



