84 INSECUTOR INSCITI^ MENSTRUUS 



America and Europe, there would be less hesitation in making 

 the synonymy aestivalis = hirsuteron. 



New data on the distribution of these forms are at hand. 

 When passing through Montana in 1917, the Yellowstone Val- 

 ley was followed, and only aldrichi was met with in the river 

 bottoms. I did not know hirsuteron from west of Minnesota, 

 and therefore the distribution of aestivalis seemed considerably 

 detached, occurring as it did only on the west of the Conti- 

 nental Divide. However, the past season the valley of the 

 Missouri was followed. Here hirsuteron occurred in Minne- 

 sota in East Grand Forks, and across the river in Grand Forks, 

 North Dakota. Without the larva it is not possible to be cer- 

 tain, but westward the specimens from Poplar and Glasgow, 

 Montana, seemed to be still hirsuteron rather than aldrichi, 

 for, though sometimes small, the mesonotal band is quite solidi- 

 fied. Still further west, at Havre, Montana, the species seemed 

 to be the same. There is therefore no very great gap between 

 hirsuteron and aestivalis, which occurs as far to the east as 

 Belton, Montana. 



These forms are, of course, all closely allied at the best. 

 It seems that hirsuteron is the stem form, with aestivalis doubt- 

 less the same, and perhaps both equal the European sticticus. 

 Aldrichi is a close derivative, adapted also to the flood-waters, 

 but intensified in habit, for it occurs in the great flood-waters 

 where the western rivers overflow wide territory, while hir- 

 suteron does not occur here, but in smaller floods. The dif- 

 ferentiation is hard to apprehend, but there seems to be un- 

 doubtedly a differentiation, for the two species do not generally 

 occur together. From hirsuteron is derived idahoensis, inhab- 

 iting the dry open tree-less portions of the river valleys, and 

 breeding in early spring pools. From idahoensis comes spenceri, 

 frequently the open grassy prairies and wholly detached from 

 the river valleys. 



Spenceri has been, from previous records, strictly a Canadian 

 species ; but it occurred to us not uncommonly in half a dozen 

 places in North Dakota and in western Minnesota. 



