376 



each basal joint of tarsus, and at apex of the other tarsal joints. Wings 

 as in Figure ii, Plate XXVII. Halteres yellow. 



Male. — Antenna slightly longer than head and rhorax taken to- 

 gether, apical joint twice as long as remaining flagellar joints together, 

 basal joint much swollen ; third palpal joint barely longer than the 

 slender second joint. Mesonotum with long hairs on spaces between 

 the vittae; no conspicuous group of hairs before wing-base, and none 

 discernible on sternopleura. Hypopygium as in Figure ii, Plate 

 XXVIII. Legs long and slender; basal joint of fore tarsus two 

 thirds as long as fore tibia, and distinctly shorter than the next two 

 joints together; mid and hind legs with long hairs, those on the tibiae 

 equal in length to about four times the tibial diameter, fourth tarsal 

 joint of all legs very much longer than fifth. 



Female. — Similar in color to the male, though generally slightly 

 darker, especially in the wing-markings. 



Length, 4.5-5 mm. 



This species has been taken in the larval and pupal stages in con- 

 siderable numbers in the Illinois River and associated waters in con- 

 nection with the work of this Laboratory on the biology of that river, 

 the following localities being represented : Copperas Creek, Thomp- 

 son's Lake, Havana, Round Prairie (near Havana), Matanzas Lake, 

 Beardstown, Fish Lake, Meredosia, Naples, La Grange, Hardin, and 

 Grafton. Imagines have been taken at Algonquin, June 24, 1895 

 (W. A. Nason) ; at Urbana, in May and July; and at Havana, in 

 April, May, and September, some being taken at light, and two reared 

 from larvae found in a rain-water barrel. Probably the species occurs 

 throughout the entire summer and fall. 



Johannsen records monilis from New Jersey, Illinois, New York, 

 and South Dakota. I have seen specimens from Plummer's Island, 

 Md., and Washington, D. C. (W. L. McAtee). 



8. Tan Y PUS illinoensis, n. sp. 



This species resembles monilis so closely that it will be sufficient to 

 indicate little more than the points of difference between them. 



Larva unidentified. 



Pupa. — (PI. XXIV, Fig. 7). Length, 6 mm. Color as in monilis. 

 The thoracic respiratory organs are similar to those of monilis, differ- 

 ing as stated in key. In monilis there is a transverse row of 3-4 

 short tubercles between the respiratory organs. It is impossible from 

 the dissections before me to say whether the two rows of short 

 tubercles, 8-10 in each row, lay transversely between the respiratory 



