534 



figure; mandibles with two moderately strong teeth and one weak 

 tooth in addition to the apical one ; anterior and posterior pseiidopods 

 stout and short, claws of posterior pair pale and inconspicuous ; dorsal 

 blood-gills stout and well developed ; anal tufts each consisting of 

 about 6 pale hairs, situated on weak papillae ; body without noticeable 

 hairs. 



Illinois locality, Illinois River at Grafton. 



This species may belong to Tanyfarsits. No attempt was made to 

 rear the species, owing to press of other work. 



Distribution of CHiRONOMiDy^ in the Ilunois River 



The principal reason for undertaking the work upon Chironomidcc, 

 the result of which is embodied in this paper, was to discover what 

 species occurred in the Illinois River and connected lakes and to de- 

 termine their distribution. Unfortunately we are not in possession of 

 data or materials to warrant any definite statement as to the distribu- 

 tion of the species prior to the opening of the Chicago Drainage Ca- 

 nal; but it is reasonably safe to assume that before that time condi- 

 tions on the upper Illinois were very similar to those on the lower por- 

 tion of the river today. When, therefore, we discover that the Chiro- 

 nomidcc occur in markedly decreasing numbers as we near the outlet 

 of the canal, where, under natural conditions, insect life should be as 

 abundant as elsewhere on the river, it is an unavoidable conclusion 

 that the comparative absence of these larvae is an indication that the 

 water is unsuited to their requirements. As previously stated ttnder 

 Chironomiis viridicoUis, the presence of "blood-worms" in any body 

 of water is not an indication that such water is polluted, although they 

 may be, and often are, found in water that is contaminated with sew- 

 age. There are, however, but few species to be found in badly pol- 

 luted water, most species being confined to unpolluted water or to that 

 which is but slightly tainted. Even blood-red larvae are not in all 

 cases found in polluted water, as the two largest species occurring in 

 the Illinois are confined to the parts of the river wdiich are compar- 

 atively clean. 



C. fcrrugincovittatus occurs principally in collections made in the 

 various lakes (Fish, Crane, Stewart's, and Thompson's), but also in 

 the channel of the river at Havana and Pekin. This is the largest 

 species, measuring on an average slightly over two inches. 



C. tcntans (?), which averages an inch in length, is much more 

 common than fcmigincovittatus and is more widely distributed, oc- 

 curring indiscriminately in lakes and in the river channel north to 



