700 CHARLES PauL ALEXANDER 
2. Brief summaries of published life histories of genera and important 
species not available for study as specimens and included here to complete 
the data. 
3. Summaries and tabulations of life-history records, larval habitats, 
economic importance, and related subjects. 
4. Keys to the families, tribes, and lesser groups. 
The adult flies are not here considered in any detail, since they have: 
been discussed by the writer in an earlier paper (Alexander, 1919 d). 
The life histories remaining to be discovered in the Nearctic fauna 
are still numerous in species, tho few in genera. There are but four or 
five genera whose life histories when made known may upset the present 
ideas on arrangement. Until more is known of these missing groups, 
they must be classified according to the adult structure. 
It will be noted that a number of important changes in nomenclature 
have been adopted in this paper. The system hitherto in vogue, based 
entirely on the structure of the imagines, was conceived by Osten Sacken 
and represented the culmination of research on the structure and affinities 
of the adult flies. A casual survey of the immature stages is sufficient 
to show the impossibility of many of the groups hitherto generally accepted. 
The principal modifications adopted in this paper are as follows: 
1. The erection of the family Tanyderidae to receive the genera 
Tanyderus and Protoplasa. These had hitherto been placed with the 
Ptychopteridae, a group to which they are not closely allied. 
2. The removal of the genus Trichocera from the Tipulidae to the 
Rhyphidae, and the inclusion of the latter family as one of the four 
existing families of crane-flies. 
3. In the Tipulidae, the elimination of four tribes — Antochini, Limno- 
philini, Dolichopezini, and Ctenophorini— as being based on a con- 
glomeration of forms referable to other tribes or else separated on an 
insufficient basis. The former tribe Antochini included members which 
the writer now refers to the Limnobiini (Antocha, Rhamphidia, 
Dicranoptycha, and other genera) and to the Eriopterini (Teucholabis, 
Elephantomyia); the Limnophilini are too close to the Hexatomini; 
and the tipuline forms constitute a very compact group which cannot 
well be subdivided into tribes. 
4. The erection of nineteen subtribes, or divisions, to include lesser 
groups of genera within the tribes. In the followmg pages these are 
