220 DISTRIBUTION OF THE MOLLUSCA IN TIME. 



16 of these 26 first appearances (comprising the 12 primi- 

 tive types) are found within the limits of the 2d fauna. 

 8 in the limits of the 3d fauna. 

 1 towards the end of the Devonian fauna. 

 1 during the Eocene period. 

 8. This diminution of the apparitions of generic types is in 

 disaccordance with the increase of the number of species 

 during the Silurian period. 



In effect, if the new types were formed by the divergence 

 of the species, as supposed by the development theory, the 

 increase of the number of specific forms must entail an 

 increase of the number of generic types. In any case it 

 could not cause a diminution of them. 



Then, each of the principal facts that we have given on the 

 subject of generic types, constitutes a grave discordance 

 between the theories of evolution and the reality. 



II. Specific Forms. 



1. We have never acquired the certainty and we have never 

 been induced to suppose that ari};^ species among the ceph- 

 alopods of Bohemia was derived by filiation and transforma- 

 tion from another anterior species. The filiation and trans- 

 formation are then, in our point of view simply theoretic 

 fictions. 



2. No species, to our knowledge, has been transformed to a new 

 generic type, neither bj- successive slow variations nor by 

 sudden changes. 



On the contrary we have ascertained at various times that 

 all the species and all the groups of the congeneric forms, 

 which have varied sensibly from their generic t^q^e in certain 

 particulars and which appeared to tend towards a new type, 

 appeared and disappeared suddenly, without leaving any 

 posterity preserving the traces of the same character. 



3. Our second phase of Fauna No. 3 possesses alone tit species 

 of cephalopods, that is to say about 31 per cent, of all the 

 species of this order known in the Silurian. Our basin, very 

 remarkable for its sinall size furnishes about 45 per cent, of 

 these. 



These accumulations of cephalopods in surfaces so restricted 

 are in contradiction with the theories of natural selection and 

 of the struggle for existence. 



III. Elements of the Shell. 



The particular study of each of the elements of the shell of 

 the cephalopods, of which we have presented a resume, shows 

 that none of them have followed a gradual variation in any one 

 direction. On the contrary, we have observed the stability of 



