Recherches snr les Poissons Fossiles, 



65 



which no longer exist* In the comparative table that is 

 shortly to be published, the names of fossil genera and of 

 species of all the geological epochs are to be indicated 

 equally with the localities in which they have been found, 

 and a particular column will be assigned to the genera cor- 

 responding with those of the present actual creation. More 

 than two-thirds of the species hitherto discovered in the 

 chalk, are referrible to genera which have entirely disappear- 

 ed ; we even here begin to find some of those singular forms 

 which prevail in the oolitic series. Nevertheless, the fishes 

 of the chalk approximate more closely than those of the 

 oolite, to the general character of the tertiary fishes; so 

 much so, that in a general approximation of geological forma- 

 tions, it appears to me more natural to associate the formation 

 of the chalk, and oi gres vert with the tertiary strata, than to 

 class them in the group of secondary beds. In the lower 

 beds of the chalk, there is no longer a single genus which 

 has living species ; and even those beds of the chalk which 

 have, contain a great number fossil. 



The oolitic series, to the lias inclusive, forms a very natural 

 and well-defined group, which ought to contain also the 

 red marl formation, in which I have not found a single spe- 

 cies referrible to the genera of the chalk. After this epoch, 

 in descending always, of the two orders which prevail in 

 the present creation, one is no longer found; while those 

 forms which are fewest in our day, are represented sud- 

 denly in very great number. As to the Ganoids, those 

 which are found here, have the genera with the symmetrical 

 caudal; and are such only as have the teeth grooved on 

 both faces, with large spinous prominent rays. For it is 

 certain now, that the great rays which Messrs. Buckland 

 and de la Beche have called Icthyodorulithes, did not be- 

 long to either Silures or Balistes ; but they are the dorsal 

 rays of large sharks, of which we find the teeth in the 

 same beds. 



K 



