411 



shorter than fifth; cmpodium as long as claws; claws simple. Wing 

 venation as in Figure i, Plate XXXV. 



Female. — Agrees with the male in color, leg characters, and vena- 

 tion. Differs in having the antenna 8-jointed and short-haired. 



Length, 3.5-5.5 mm. _ 



Illinois localities : Illinois River at various points near Havana — 

 larvae common ; Urbana, April 2, 1889 (John Marten), imago (male) 

 — the only adult I have seen from this state. 



Originally described from Europe and since recorded from New 

 York, Idaho. Washington State, and Greenland. I have seen speci- 

 mens from Plummer's Island, Md., April 28, 1907; from Denver, 

 Colo., December 27, 1909, and from Montana. The last-mentioned 

 specimens were taken by Dr. C. C. Adams at the snow-line on the 

 mountains, where the females were ovipositing in the pools formed 

 close to the melting snow. Johannsen records the larvae as occurring 

 "among the algai on the surface of rocks over which the water flows 

 rapidly." The larv?e in the collection here were taken when dredging 

 in the Illinois River. 



Thai^assomyia Schiner 



This genus is separable from Ortlwdadius by the structure of the 

 tarsi, the fourth joint being distinctly shorter than the fifth and ob- 

 cordate. The type species of the genus, franenfeldi Schiner, has 

 been found by Swainson "on Obelia zoophytes growing at the end of 

 St. Anne's pier." This record refers to the occurrence in sea water."* 

 Johannsen describes the larva, pupa, and imago of T. obscitra from 

 Ithaca, N. Y. 



Thalassomyia obscura Johannsen 



Thalassomijia ohscura Johannsen, Bull. 68, N. Y. State Mus., 1903, p. 437. 



Pcinale. — Black, opaque. Head black, face and scape of antennae 

 yellow. Thorax black on disc, pronotum and a large spot on each 

 unterior lateral angle yellow, the spaces between vitt?e paler than vittae, 

 pleune mostly yellow, sternopleura and some smaller spots above it 

 brownish; scutellum brown. Basal two segments of rbdomen yellow, 

 the others with indistinct pale posterior margins; venter yellow, in- 

 fuscated at apex. Legs black, fore coxee and trochanters and bases of 

 femora of all legs yellow. Wings clear, veins brown. Halteres yel- 

 low. 



*"An Account of British Flies," by Theobald, p. 202. 1892, 



