THE JURASSIC AGE. 



Mammifers . 



Birds 



Beptiles 



Fishes 



Crustacea 



Insects 



Mollusca and Radiata 



Orders. 

 11 

 6 

 2 

 3 

 2 

 1 

 7 



32 



During this age nearly 300 new generic forms were called into 

 existence, of which about 180 did not survive the age. This 

 fauna consisted of about 4000 species, which were distributed 

 among the ten periods, so that, save in very exceptional cases, no 

 species are common to any two periods. Each period, therefore, 

 had its own peculiar and characteristic animal kingdom. 



324. To illustrate this remarkable principle, which seems to 

 have been adhered to in all the operations of creative power from 

 the first animalisation of the globe to the present period, we here 

 subjoin a tabular synopsis, showing the number of species 

 Mollusca and Radiata found in each of the ten stages, and also th 

 number common to two or more stages. 



But in the second column the same species is frequently 

 repeated. Allowing for this, the total number of species which 

 are found in more than one stage is only 56, or about 1^ per cent, 

 of the entire number, a proportion which is altogether insig- 

 nificant, and which cannot be considered as impairing the general 

 law that each period had its own specific fauna. 



325. From a general analysis of the facts, the following con- 

 clusions may be deduced : 



1st. That during the Jurassic age of the world about 4000 

 specific animal forms lived, different from any which existed at 

 any antecedent or posterior epoch. 



2nd. That this total number consisted of ten distinct groups, 



69 



