504 



Pupa. — Length 3-4 mm. Yellow, the black markings of the en- 

 closed imago showing through (PI. XXXII, Fig. 7). Thoracic respir- 

 atory organs slender, tapering, inconspicuous, their surfaces without 

 distinct hairs ; several long and slender hairs on pronotum and a few 

 on disc of mesonotum. Abdomen with the dorsal segments covered 

 with minute setul?e except on some small rounded areas on disc of each 

 segment, the usual apical transverse series of strong setulae on second 

 segment, and a transverse preapical patch of weaker and broader ones 

 on the other segments ; apical appendages short and rather slender, 

 armed apically with three long hairs. 



Imago; Male. — Yellow, shining. Head yellow, scape of antennse 

 black, flagellum and palpi fuscous, antennal plumes yellowish brown. 

 Mesonotum with glossy black vittse which are sometimes confluent and 

 obscure the ground color ; pleurae with a large black patch on sterno- 

 pleura and a smaller one before wing-base ; scutellum and postnotum 

 opaque black. Abdomen either opaque black with first, fourth, and 

 seventh segments and apical half of hypopygium yellow, or yellow 

 with second, fifth, and sixth segments, except their anterior fourth, 

 the whole of eighth segment, and a spot on disc of fourth black. Legs 

 whitish yellow, conspicuously blackened on all knee joints and apices 

 of tibise ; fore tarsi black, mid pair blackened from near base of second 

 joint to apex of fifth, hind pair from before apex of third to apex of 

 fifth. Wings clear, veins yellowish. Halteres pale yellow. 



Antenna slightly longer than head and thorax together. Prono- 

 tum rather broad, its breadth almost uniform throughout. Apical por- 

 tion of lateral arm of hypopygium as in Figure 2, Plate XXXVII. 

 Fore tarsi without conspicuous hairs, basal joint more than half as 

 long as fore tibiae (30:53), second joint half as long as basal (15). 

 Third vein ends at beginning of apical curve of wing; cross vein 

 slightly proximad of wing-middle ; cubitus forking distinctly beyond 

 cross vein. 



Female. — Agrees in color with the male. 



Structurally also very similar, but the wings are rather broader 

 and the legs slightly stouter. 



Length, 3-4 mm. 



Illinois localities : Illinois River at Havana — abundant, the eggs 

 sometimes fovmd in immense numbers floating in a large gelatinous 

 mass — Grand Tower, Dubois, Golconda, Peoria, iMomence, Rock 

 Island, Urbana, Aluncie. Probably the species occurs throughout the 

 state. Dates of occurrence range from April 18 to October 20. 



Originally described from Europe. Previously recorded by 

 Johannsen from New York and Chicago. I have seen a specimen taken 

 on prairie flowers at Moscow^ Idaho, by Professor Aldrich. 



