312. On the Diptera of the Amber-fauna, 
number of species has increased, or even what new forms have 
been added to the previously existing ones, such a comparison 
would of course afiord the highest interest. But, unfortunately, 
such an attempt is impossible, on the one side because of the 
as yet very imperfect knowledge of the now living Diptera, on 
the other, because what we know of the Amber-Diptera is but a 
fragment of a district fauna. In confronting, therefore, both 
faunas, I will by no means try to discover and to establish dif 
ferences between them of the above indicated kind, which would 
be a useless attempt; my only aim will be to refute as erroneous 
certain conclusions as to the existence of such differences, 
as founded upon erroneous premises. Fora long time students 
its close relationship to Electra. Both combine the many-jointed 
antenne of the Diplera nemocera with the general structure of 
eed some reason to suppose that the limit between 
two sections was sharper now than in the Tertiary period, al- 
though our very incomplete knowledge of the living Dips 
caution was justified subsequently by the discovery of a Bost 
American species, published by Mr. Haliday under the name 
Rachicerus julvicollis, a species which not only forms a most - 
cided transition between the two principal sections of Diptet™ 
but shows even the closest relationship with Hlectra and Chryso- 
themis. My own studies of the North American fauna have 
