700 Charles Paul Alexander 



2. Brief summaries of published life histories of genera and important 

 species not availal^le 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 tletail, 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 TipuUdae, the eUmination 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 



