310 £L. Agassiz on Animals in Geological Times. 
with sufficient care and proper allowance is made for the limited 
time during which investigations of fossils have been traced com- 
pared with that which has been almost everywhere devoted to 
the closer study of living animals, it will be seen that the number 
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 faunze ofall 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 faunze which have 
yielded much larger numbers of species, presenting a greater Var 
riety 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 six hundred. About six 
hundred species is again the number assigned to the whole basin 
of: the Mediterranean, including both the European and Afnican 
coasts. Now the most superficial comparison between them an 
the fossil species which occur in the lower tertiary beds in the 
vicinity of Paris, shows the latter to exceed twice that number; 
there are indeed twelve hundred species of fossil shells now 
known from the eocene beds in the immediate vicinity of Paris, 
affording, at once, a very striking evidence of the greater diver- 
sity and greater number of species of that geological period when 
compared even with those of a wider geographical area at the 
present aay. ; 
If it be objected that the variety of forms which oceur in trop 
cal faune is greater than that which we observe on the shores of 
our temperate regions, and that the temperature of the teruiary 
period having been warmer we may expect a larger number 
fossil species from those deposits, 1 would only refer to local enu- 
merations of marine shells from several tropical regions, to sustain 
my assertion that the number of fossil shells of 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 three huudred species of shells given by 
Dufo as occurring around the Sechelles Islands, the extent of 
of the Red Sea by Hemprich, Ehrenberg and Riippel, and there 
