THE PEE -ADAMITE EARTH. 



556. To convey an approximate estimate of this fauna, we have 

 collected and arranged, from the data supplied by M. D'Orbigny, 

 in the following table a synopsis of the total number of generic 

 forms of each class. 



Synopsis of the generic forms included in all the fauna (exclusive of 

 the Annulata), from the first animalisation of the earth to the human 

 period inclusively. 



557. It appears from this, that so far as observation has supplied 

 data for such an estimate, the total number of generic animal 

 forms which have been called into being, since the first animalisa- 

 tion of the earth to the present time, has been 2800. Of this 

 number, 1327, or nearly the half, were created at the commence- 

 ment of the human period, a large proportion for one period out 

 of thirty. It must be observed, however, that it is extremely 

 improbable that the number of genera in past periods is as well 

 ascertained as in the present. In the one case we have the living 

 creation to count from ; in the other we have nothing but the 

 buried remains of the fauna of each period. 



Of the number of genera, 1473, that lived in previous ages, 

 only 540 have reappeared. There are therefore 933 generic forms 

 unknown to the present fauna. These, as we have seen, however, 

 154 



