42 PROCEEDINGS OF THE NATIONAL MUSEUM vol. loe 



Remarks: The yellowish body color, the whig banding, and the 

 male genitalia separate this species from other Rivellia. 



RivpUia pallida Loew 



Figure 3,e-h 

 Rivellia pallida Loew, 1873, p. 95, pi. 8, fig. 8. — Hendel, 1914a, p. 181. 



Type locality: Washington, D. C. (MCZ). 



Males: Body length 3.5-4.5 mm. 



Head : Frons yellow to brownish yellow ; upper fronto-orbital plates 

 concoloroiis with frons, ocellar triangle blackened. Face with dorsal 

 half priiinose, ventral half shining, smooth, yellow to brownish yellow; 

 parafacials and part of orbits ventral to each eye yellow to brownish 

 yellow. Antenna with first and second segments yellow to brownish 

 yellow: third segment blackened anteriorly or on outside, remainder 

 yellow, the tip pointed anteriorly. Anteclypeus concolorous with 

 ventral portion of face. Palpi yellow. Postcranium yellow to brown- 

 ish yellow, pruinose. 



Thorax: Mesonotum yeUow to brownish yellow; strong humeral 

 and posterior dorsocentral setae present. Scutellum and postscutel- 

 lum concolorous with mesonotum. Pleura yellow to brownish yellow, 

 mostly shining, pruinosity obscure except on laterotergite. Meso- 

 pleuron with scattered pale and black setae on posterior one-thnd; 

 sternopleuron with few scattered pale setae on disc; pteropleuron 

 with few scattered pale setae on disc, few black setae present ventral 

 to subalar. Laterotergite completely pruinose. Prosternum yeUow. 



Thoracic appendages: All legs with coxae and femora yellow. 

 All tibiae yellow or sometimes brownish. Front and hind tarsi 

 wholly yellow or blackened from third or fourth segment; middle 

 tarsi wholly yellow, blackened from thu'd or fourth segment, or only 

 fifth segment blackened. 



Wing (fig. 3,e) length 2.5-3.5 mm. Bands black. First and 

 second bands separated at costal margin; third and fourth bands 

 narrowly joined at costal margin; second and third bands sometimes 

 almost joined in discal cell. The part of first basal cell contiguous 

 to second basal cell completely hyaline or faintly banded at base. 

 Section of fourth vein proximad of anterior crossvein with slight 

 bend. Halteres brownish yellow to brown. 



Abdomen: Tergites shining, smooth, yellow, bro\vnish yellow, or 

 yellowish brown, somxCtimes with reddish or blackish blotches. Disc 

 of first tergite with pale setae. Genitalia (fig. 3,g,h) with apical part 

 of aedeagus longer than basal part, appearing appressed to basal part 

 at base. From dorsal view, lateral margins of apical part rounded 

 basally and gradually converging apically. 



