459 



of all tibiae, apices of fore tibicT, almost the entire fore tarsi, the last 

 3-4 joints of mid and hind tarsi, and the narrow apices of mid and 

 hind tibi« brownish. Wings clear, veins yellowish, cross vein in- 

 fuscated. Halteres yellow. 



Frontal tubercles distinct ; antenna slightly longer than head and 

 thorax combined. Hypopygiimi similar to that of decorus (PI. 

 XXXIII, Fig. 11). Legs slender; fore tarsi without long hairs, basal 

 joint less than one half fonger than fore tibiae (90 : 65) ; mid and hind 

 legs with moderately long hairs. Third and fourth veins ending about 

 an equal distance from apex of wing ; cubitus forking almost below 

 cross vein. 



Female. — Agrees with the male in color. 



Length, 7-8 mm. 



Illinois localities: Champaign, Urbana, Chicago (Thirty-ninth 

 Street Pumping Station), Havana, and various points on the Illinois 

 River as far north as Marseilles, above the dam, April, June, and No- 

 vember. 



This European species has been reported from New Jersey 

 (Johnson) and from Ithaca, N. Y. (Johannsen). I have seen speci- 

 mens from Pennsylvania and Maryland. 



The larvse of znridieollis were found in the reservoir for the supply 

 of the city water of Champaign, 111., by the writer December 29, 1914- 

 They were nearly full-grown at that time, although several specimens 

 were found whose size would have indicated probably but six^ or 

 seven days' growth under normal summer conditions. It is possible 

 that these small specimens were retarded in growth by the advent of 

 cold weather, though it is not impossible that they were the result of 

 p^edogenesis, which occurs in allied genera. The absence of oxygen or 

 its comparative scarcity in water obtained from deep wells can have 

 little or no detrimental effect upon larvae of this species or its allies, 

 since they are found at great depths in lakes where there is scarcely 

 any oxygen; and the presence of algae and diatoms in wells, even of 

 considerable depth, secures to the larvae an abundance of their prin- 

 cipal food. It being practicably impossible to prevent these insects from 

 obtaining access to reservoirs and wells, measures must be taken 

 periodically for their reduction or extermination. This is a difficult 

 problem in the case of large reservoirs, and it is still more difficult to 

 protect wells. Here the introduction of certain species of fish may be 

 a successful measure — a course not possible, however, where large 

 quantities of water are drawn off by pipes, even if these have perfo- 

 rated caps, since very small fish would, notwithstanding, pass into the 

 pipes and cause more trouble than the chironomids. 



