Number of Animals in Geological Times. 35 1 



pared with that which has been almost everywhere devoted to 

 the careful study of living animals, it will be seen that the num- 

 ber and diversity of species peculiar to each special fossil fauna 

 is, in most instances, equal to those found to characterize zoological 

 provinces of similar boundaries at the present day. And this 

 may be said of the fossil fauna? of all ages. In many instances 

 the result is even quite the reverse of what is generally supposed 

 to be the fact, for there are distinct fossil faunae which have 

 yielded much larger numbers of species, presenting a greater 

 variety of types than any corresponding fauna in the present age. 

 Some examples will justify this perhaps unexpected statement. 



The number of species of shells which are found living along 

 the shores of Europe does not exceed 600. About 600 species, 

 again, is the number assigned to the whole basin of the Mediter- 

 ranean, including both the European and African coasts. Now 

 the most superficial comparison between them and the fossil 

 species which occur in the lower tertiary beds in the vicinity of 

 Paris, shows the latter to exceed twice that number; in fact, 

 1200 species of fossil shells are now known from the eocene 

 beds in the immediate vicinity of Paris, affording at once a very 

 striking evidence of the existence of a greater diversity and 

 greater number of species at that geological period, even when 

 compared with those of a wider geographical area, than at the 

 present day. 



If it be objected that the variety of forms which occur in tro- 

 pical faunae is greater than that which we observe on the shores 

 of our temperate regions, and that the temperature of the tertiary 

 period having been warmer we may expect a larger number of 

 fossil species from those deposits, I would only refer to local 

 enumerations of marine shells from several tropical regions to 

 sustain my assertion, that the number of fossil shells from the 

 eocene beds of the immediate vicinity of Paris, is much greater 

 than that of any local fauna of the present period, even within 

 the tropics. A catalogue of not quite 300 species of shells given 

 by Dufo as occurring around the Seychelles Islands, the extent 

 of which may fairly be compared with that of the lower tertiary 

 beds around Paris, will suffice to show, that, in a tropical local 

 fauna, the number of species known to exist in the present day 

 is far inferior to the number of species known to have existed 

 during the deposition of the lower tertiary beds in the vicinity 

 of Paris. Another catalogue by Sganzin, of the shells found 

 about Mauritius, Bourbon and Madagascar, gives also less than 

 300 species for the extensive range of seas surrounding those 

 islands. Let us fm-ther compare the results of the investigations 

 of the shells of the Red Sea by Hemprich, Ehrenberg and Riip- 

 pell, and there again we find a smaller number, and a more limited 



