Fossil Fishes. 41 



a 



ing the prodigious number of living species to which they approxi- 

 mate, it is often very difficult, in the condition in which they are 

 discovered, to identify them, or rather exactly to appreciate their 

 distinctive characters. I will only remark, in general, that up to 

 the present moment, I have not found a single species which is per- 

 fectly identical with those of our seas, except that little fish which 

 is found in Greenland, in the geodian clay, and the geological age of 

 which is unknown to me. 



" The species of the Crag of Norfolk, of the superior subapennine 

 formation, and of the molasse formation, for the most part approach 

 to the common genera of tropical seas ; such as the Platax, the 

 Great Carcharias, the Great Myliobates, &c. 



In the inferior tertiary formations, — in the London clay, the 

 coarse limestone of Paris, and of Monte-Bolca, we find that at least 

 a third of the species already belong to genera which no longer ex- 

 ist. In the comparative tables of all known fishes which I propose 

 soon to publish, I shall give the names of all the fossil genera and 

 species of all geological epochs, and at the same time shall point out 

 all the localities in which they are found, and the corresponding ge- 

 nera of the actual existing creation, in a separate column. 



The Chalk group includes more than two-thirds of those spe- 

 cies which are referable to genera which have entirely disappeared ; 

 and here we already see some of those singular forms which prevail 

 in the oolite series. At the same time, as a whole, the fishes of the 

 chalk formation much more resemble the general character of the 

 fishes of the tertiary series than that of those belonging to the oolite 

 group ; and this to such an extent, that did I regard only the fishes, 

 in a general classification of geological formations, it would appear 

 to me more natural to associate the chalk and greensand series with 

 the tertiary formations, than to rank them with the secondary rocks. 

 Underneath the chalk there is no longer a single genus which pos- 

 sesses existing species ; and even those of the chalk which have 

 them, possess a much greater number of fossil ones. 



"The oolite group to the lias, also included, forms a very natural 

 and very well defined series, which must also comprehend the Weal- 

 den rocks, in which I have not found a single species referable even 

 to the chalk genera. From that epoch, always descending, the two 

 orders which prevail in the present creation are no longer found, 

 whilst those which are in small numbers in our days suddenly present 

 themselves in great abundance. As to the Ganoi'des, the genera with 



Vol. XXX.— No. 1. 6 



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