366 



10. Apical half of each of the abdominal appendages very slender, the 



breadth of each at base of that part not over one third the length 

 of apical half 11 



— Apical half of abdominal appendage about equal in length to its 



breadth at base of that part 12 



11. Abdominal appendages twice as long as their combined basal 



breadth Tanypus decoloratus (p. 370) . 



— Abdominal appendages one fifth longer than their combined basal 



breadth Tanypus carneus* (p. 378) . 



12. Thoracic respiratory organ about three times as long as its great- 



est diameter, small and inconspicuous Tanypus fastuosus. 



— Thoracic respiratory organ more than three times as long as its 



greatest diameter, long and conspicuous. T any pits dyari (p. 380). 



13. Apex of respiratory organ bell-shaped (PL XXVII, Fig. 4) ; 



margin of abdominal appendage with over 100 short hairs 



Procladius concinnus (p. 394) . 



— Apex of respiratory organ not bell-shaped (PL XXVII, Fig. 9) ; 



abdominal appendage with few marginal hairs (PL XXVI, Fig. 

 12) Protentlies hellus (p. 388). 



Tanypus Meigen 



The species belonging to this genus are readily separable from 

 those in ProcladHus by the presence of hairs on the surface of the 

 wings, and from Protentlies by the sessile cubitus. 



I give a key to the Illinois species in the Laboratory collection, and 

 descriptions by means of which they may be separated from other 

 North American species which have not yet been taken in this state. 

 As in other genera, it is highly probable that many species occur in 

 Illinois which are not represented in the collection before me, but 

 from lack of examples of already described species and to avoid 

 extending this paper on the uncertain basis of the slender clues 

 afforded by some of the descriptions — such course being usually dis- 

 astrous — I have not attempted to present a key to all the described 

 North American species. 



Key to Species 



1. Wings without dark spots or bands, at most the cross vein black- 



ened 2 



— Wings with distinct dark spots or bands 7 



2. Large dark species, 4-5 mm. ; thorax with brown vittffi which are 



rather spotlike ; cross vein of wings conspicuously blackened .... 

 1. Jiirtipennis. 



*This distinction is based upon a comparison of a mounted specimen of decolor- 

 atus with Johaunsen 's figure of carneus. 



