316 On the Diptera of the Amber-fauna. 
result in the course of my researches took place as follows. It 
appeared at first that the living species of the indicated kind 
were scattered irregularly and at random over all the parts of the 
globe. Further inquiry not only increased the number of suc 
related couples of species, but allowed also very frequently to 
replace the living species of some previously discovered pair 
some other, still more closely allied to the fossil one. The fur- 
ther the research was pursued in this direction, the more it be- 
came evident that the living species of these pairs have a very 
definite geographical distribution, as being gradually eliminated 
from the other parts of the world, they tended more and more 
to concentrate in Europe, and in a much higher degree in North 
America. ; 
I readily acknowledge that my researches have necessarily 
been influenced by a purely personal coéfficient, which has to be 
taken into account, in order to establish the absolute value of 
the result obtained. This personal coéfficient consists in the at- 
meric proportion of the living species from different parts of the 
world, which could be subjected to comparison, as well as in the 
more or less complete knowledge I had of the Dipterous faunz 
of the different continents. The European Dipterous fauna 8 
naturally the best known to me; next comes the North Ameri 
eam fauna, which I know better than that of all other extra 
European countries, excepting perhaps that of the Cape, as. 
possess from that region more than 800 species, collected within 
a comparatively limited territory. It is therefore unquestionable 
that the result obtained by me requires a correction, at 
can have a claim to an absolute value. But should I even it 
troduce this correction in the highest measure admissible, st 
enough will be left to enable me to assert with the utmost cer 
tainty that those among the living Diptera which most closely 
resemble the amber Diptera, abound in a most prevailing degree 
in North America and especially between the latitudes of about 
some amber Diptera are more allied than to any other know? 
living species. 
The facts just explained become especially striking through 
the circumstance that those genera of amber Diptera, whit 
not occur in Europe, and which for this reason attracted i 
attention from European students, were in part discovered 12 
re i : 
America, and are in replaced there by closely allied gener. 
With regard to this, I 
M will remind only of what has beet a 
above on the genera Diplonema, Toxorhina, Styringomy ”” 
