399 



been kept in view is principally that of presenting a classification 

 whereby the Chironouiidcv occurring within the State of Illinois may 

 be readily identified. It has, however, been necessary, particularly in 

 this subfamily, to examine a large number of species which are not 

 represented in the collection of the State Laboratory of Natural His- 

 tory, and this paper presents certain facts ascertained from an exam- 

 ination of species not known to occur in the state because they seem 

 to support deductions arrived at from an examination of Illinois 

 species. 



The larvae of the different genera are very similar in appearance 

 and, as already indicated, do not seem to lend themselves to generic 

 classification. The "blood-worms" do not belong exclusively to the 

 genus Chironomus, as some species of Tanypince are blood-red. It is 

 not the case that red larvae have invariably ventral blood-gills on the 

 eleventh segment in the genus Chironomus as stated by Johannsen.* 

 Several blood-red species of Chironomus have no ventral blood-gills, 

 though I do not know of any species of another color which possesses 

 these organs. 



I have included in a single key all the larv^ of this subfamily 

 known to me, considering it probable that they may thus be more read- 

 ily identified. 



The pupse of the genus Chironomus are readily separable from 

 those of any other genus by the numerous hairlike filaments of the 

 thoracic respiratory organs. The other genera, however, are very 

 similar in general appearance, and, considering the small number of 

 species which I have examined that are represented in all stages, it 

 would be unwise to propose in this paper any method of separation of 

 the pupje on a generic basis. That characters exist which irjay be used 

 for the purpose of generic subdivisions I have no doubt, but no ad- 

 vantage is to be gained by such a course when the paucity of available 

 data would in all probability lead to a confusion of generic and spe- 

 cific characters. 



The imagines of some genera are very closely allied to each other, 

 and in certain cases, Camptocladius and Orthocladins, for example, 

 the genera are almost inseparable. I have endeavored to^ make the dis- 

 tinctions clear, and have refrained from elaboration in description, 

 depending largely on illustrations, vvhich are more easily comprehen- 

 sible than the most lucid description. Many characters which have 

 either been ignored or overlooked by previous writers on the famdy 

 have been introduced in this paper,' but the anatomical details have 

 by no means been exhausted. 



* Aquatic Nematocerous Diptera, Bull. 86, N. Y. State Mus., 1905, p. 181. 



