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4 
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and Number of Animals in Geological Times. 281 
basin of the Mediterranean, excluding the minute species 
which have not yet been sought for among the fossils. 
In earlier geological ages, during the deposition of the 
coal and other palozoic rocks, the class of Crustacea pre- 
sents a very different character. The gigantic Entomostraca, 
and the extinct family of Trilobites, take the place of the lob- 
sters and crabs of later periods. But paleontological works 
illustrating the fossils of Sweden, Russia, Bohemia, England 
and France, have made us acquainted with as great a variety 
of species of those families as are found of the later repre- 
sentatives of the class in more modern deposits. So that 
among Articulata the class of Crustacea can be said to have 
been, at all periods, as largely represented, and to have shown 
as great a variety of forms as occur anywhere within similar 
limits in the present time. 
The carcinological fauna of the whole Indian Ocean scarcely 
exceeds in variety or number of species that of Bohemia alone, 
as it is now known by the admirable investigations of M. 
Barrande. 
From their minuteness and general structure, Insects might 
be excepted in such a comparison without affording a sufh- 
cient argument against the view I have taken of the subject, 
even if insects had nowhere been found in large numbers in 
a fossil state. For it must be plain that their preservation 
requires more favourable circumstances than the preservation 
of other animals more largely provided with solid parts. But 
though the fossil insects have not been sufficiently investi- 
gated in all geological formations, have we not several ex- 
amples which show that in some geological periods, at least, 
they were as numerous as in the present day? The beautiful 
Monograph of Behrens, of the insects which occur in Amber, 
shows how varied these animals were during the period of 
the formation of that gum; and the unparalleled investiga- 
tions of Professor Oswald Heer upon the insects of Oeningen 
and Radeboy have furnished us with means of comparison, 
which show that during the deposition of the Molasse of 
Switzerland, the insects were as numerous and as diversified 
there as they are anywhere in our day, within similar boun- 
