164 
of the numerous forms of Tipulidz recognized by Loew in Prus- 
sian amber, we should now have a far better basis for some exact 
knowledge of the past. 
Up to the present time the only known fossil Tipulide from 
America were the few which I have published from the Green 
River beds in Wyoming, and the White River beds in western 
Colorado. In preparing the present memoir these have been sub- 
jected to a fresh study by comparison with those at Florissant, though 
I have not attempted to extend our knowledge of the fauna of 
these deposits, but have merely described the Florissant species, 
and introduced those known from other localities in their proper 
systematic position. In doing this the number of the previously 
described types has been reduced by two, and there remain six 
species of four genera of Limnobinz from White River, and two 
species of one genus of Tipuline from Green River. Other 
species are in my possession which will be published on a future 
occasion. 
The new forms here described come, as stated, from Florissant 
only, and number twenty-nine species of ten genera of Limnobine, 
and twenty-two species of five genera of Tipulinz. No such 
extensive addition to tertiary Tipulidez has been made since Loew 
first indicated the riches (still unpublished, after the lapse of forty- 
three years) of the amber fauna of Europe. If we were to com- 
pare the now described and figured tertiary species of America 
with the actually described or figured tertiary species of Europe 
(seventeen species of seven genera of Limnobinz, eleven species of 
three genera of Tipulinze), we should find twice as many Limno- 
bing, and more than twice as many Tipulinz; or a Tipulid fauna 
considerably more than twice as rich as that of Europe. 
In a memoir on the Zerteary Rhynchophorous Coleoptera of North 
America, now passing through the press (Monograph xxi, U. S. 
Geological Survey), I have called attention to the fact that not 
a single one of the one hundred and sixteen species of weevils 
found fossil at Florissant occurs in any of the three other prolific 
localities of fossil insects in Colorado and Wyoming ; while each of 
these three (Roan Mountains, in western Colorado ; White River, 
at the boundary between Colorado and Utah; and Green River, 
Wyoming—which together possess seventy-five species) shares from 
one third to two thirds its species with one or the other of its neigh- 
bors. From these facts, and from the field evidence, I have drawn 
