308 On the Diptera of the Amber-fauna. 
from their examination, to form a catalogue of the species which, 
under the above supposition, might be considered as belonging to 
the same district-fauna. Some very beautiful pieces of amber, 
containing each from ten to twelve species of Diptera have 
greatly aided me in this investigation. But among most of the 
amber collectors the unfortunate fashior prevails of dividing the 
larger pieces, containing several specimens, into smaller fragments 
in order to show each one by itself and to make a more conven- 
ient arrangement in the museum. The loss to a true scientific 
investigation of the Amber-fauna by this mode of proceeding 
has been so great that I cannot use too strong language in pro- 
testing against it. Although the catalogue thus formed does not 
by any means embrace all the species, it is yet comprehensive 
enough to enable me fully to confirm the supposition that the 
Diptera which are found in Prussian amber belong to one and 
the same district-fauna. 
The assumption that the Amber-diptera represent a fragment 
only of such a district-fauna, dependent upon special and yet 
uniform local conditions, must be considered as established, if 
e composition of this fauna evidently suggests coincident con- 
clusions as to the nature of these local conditions; or, in other 
words, if it can be proved that the Dipterous fauna of the am- 
ber is composed of the different families, just in the same man- 
ner as families of recent Diptera would enter into the composition 
of a fauna, subject to certain local conditions. ; 
_ Now, the composition of the Dipterous fauna of the amber 18 
indeed precisely such, as forcibly to suggest some conclusions 
about the nature of the localities in which it flourished and 10 
up with vegetation, or the shelter of the denser forests, 80. 
they are found in abundance in amber. Of the Dolichopodid@, 
those species are quite absent which live principally pon | 
water, or on water plants, while of those more active forms 
which swarm in open spots, there are only a few scattered bod 
Sentatives; on the contrary, of those genera whose species 2 “ 
present day are found lurking for their prey in swarms on ™ 
