FLIES OF GENUS RIVELLIA — NAMBA 29 



shining disc, borders narrowly pruinose. Laterotergite completely 

 and densely pruinose, Prosternum black. 



Thoracic appendages: Front legs: Coxae and femora yellow; tibiae 

 wholly yellow, yellow at base and gradually blackened toward tip, 

 wholly dark brown, or wholly black; tarsi unicolorous, varying from 

 yellow to dark brown, never darker than tibiae. Middle legs: Coxae 

 dark brown; femora yellow; tibiae yellow at extreme base, remainder 

 dark brown or black; tarsi wholly yellow. Hind legs: Coxae with 

 brown spot at base on outside, remainder yellow; femora yellowish 

 brown at tip, remainder yellow; tibiae dark brown or black; tarsi 

 blackened from thu-d segment, remaming segm.ents yellow. 



Wing (fig. 1,^) length 2.9-3.7 mm. Bands black, very broad. 

 First and second bands widely separated at costal margm, joined 

 broadly posterior to third vein; third and fourth bands broadly joined 

 at costal margin. Second and thu-d bands appear perpendicular to 

 costal margin. First basal cell completely banded. Section of fourth 

 vein proximad of anterior crossvein almost straight. I have seen one 

 specimen with second and third bands joined in the discal cell. 

 Hal teres brownish yeUow or brown. 



Abdomen: Tergites shinmg, rugose. The color pattern varies 

 somewhat. Usually with a dark brown transverse band at base next 

 to thorax, remamder of first, and the second and third tergites yellow- 

 ish except for a dark brown median longitudinal band on thh'd tergite. 

 Kemaining tergites dark brown or blackish green. Basal transverse 

 band sometimes absent, median longitudinal band on third tergite 

 sometimes absent, both sometimes absent. Disc of fu*st tergite with 

 pale setae. GenitaUa (fig. l,i,j) with apical part of aedeagus conical 

 in shape, the two filamentous terminal tubes little shorter than base 

 of apical part. 



Females: Body length 3.8-5.0 mm.; wing length 3.1-4.0 mm. 

 Ovipositor sheath black. Otherwise similar to males. 



Specimens examined: Iowa (1099, IScTcf): Amana, Clmton, 

 Counties 3, 34, Pleasant Valley; June 22-Aug. 12. Manitoba (19): 

 Winnipeg; Aug. 21. Minnesota (8699, 54<:?'cf): Big Stone 

 County, Madison, Olmsted County, Mine dump on north bank of 

 Snake River 4 miles east of Pme City, Mouth of Snake River (Pine 

 County), St. Anthony Park (Ramsey County), Rock County, Sher- 

 burn; May 19-Aug. 16. Montana (19,3 cT cf): No data. Nebraska 

 (19, Icf): Valentine; June 11. North Dakota (2d'cr): White, 

 Winner; July 4-12. 



Remarks : The banding of the wings distmguishes this species from 

 other Rivellia. Numerous specimens of this species were caught 

 along a riverbank on Carex aguatilis Wahlenb. 



