166 
proportion of the genera are extinct (genera which include about 
one third of the species), and of the remainder the larger proportion 
are genera found in north temperate regions of both worlds. 
Cladura only (with the allied extinct Cladoneura) shows dis- 
tinctively American affinities, and none are more nearly allied to 
the genera of the European fauna, whether recent or extinct, than 
to those of the existing American fauna. 
In making a comparison between our tertiary Tipulid fauna and 
that of North America north of Mexico on the one hand, and 
the more imperfectly known fauna of the southern part of North 
America * on the other, the tertiary fauna distinctly appears more 
nearly related to the former, for the latter contains the following 
only: Limnobini, 1 sp.; Rhamphidini, 3 sp.; Eriopterini, 3 sp.; 
Limnophilini, 6 sp.; and Anisomerini, 7 sp., a total of twenty Lim- 
nobine ; and there are besides eighteen Tipulinee. ‘The relative 
proportion of Tipulinee is therefore much greater ; while amcng the 
Limnobine the tribe Anisomerini, not represented at all among 
the fossils (and having in the United States and Canada but six 
per cent. of the species, if the tribes represented in Mexico and 
Central America alone are counted) possesses no less than thirty-five 
per cent. of all Limnobine, while the Limnobini have but five per 
cent. It is only in the relative numbers of the Rhamphidini that 
any nearer approach is seen between the tertiary fauna of Colorado 
and the present Central American fauna. 
Nor, if we examine the genera separately, can we come to any 
different -result, for while the fossils show in several instances an 
identity with or close affinity to those found in the United States, 
the only genera among them which are also represented in the Cen- 
tral American fauna are the widespread and prolific types, Limno- 
phila (sens. lat.) and Tipula; and not a single other genus found in 
the south shows any particular affinity to the extinct forms. Weare 
forced to conclude, therefore, that the general affinities of the fossils 
are with the existing fauna of the general region in which they are 
found. The distribution, however, of the living genera in the 
United States is too little known to permit any definite and de- 
cisive conclusions on this latter point. 
The relative representation in species of the different groups of 
Limnobine and of the total number of Limnobine and Tipulinz 
in different regions in past and present times is shown in the follow- 
* As given in Baron Osten Sacken’s contribution to the Biologia Centrali- Americana. 
