ee 
and Number of Animals in Geological Times. 278 
may be, it has been restricted, for each geological formation, 
to a few circumscribed areas. Comparisons of fossils with 
the living animals ought, therefore, to be limited to geogra- 
phical districts corresponding in extent to those in which the 
fossils occur ; or, more properly, a fossil fauna with all its 
local pecularities ought to be compared with a corresponding 
fauna of the present period, and not with al/ the animals of 
the same class living at present upon the whole surface ot 
the globe. And when this is done with sufficient care, and 
proper allowance is made for the limited time during which 
investigations of fossils have been traced compared 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 pro- 
vinces of similar boundaries at the present day. And this 
may be said of the fossil faune of all ages. -In many instances 
the result is even quite the reverse of what is generally sup- 
posed to be the fact, for there are distinct fossil faunze 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 unex- 
pected. 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 African coasts. Now the most superficial com- 
parison 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 ; 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 diversity and greater 
number of species of that geological period when compared 
even with those of a wider geographical area at the present 
day. | , 
If it be objected that the variety of forms which occur in 
tropical faunz is greater than that which we observe on the 
VOL. LVII. NO. CXIV.—OCTOBER 1854. 8 
