22 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.65 



24. Eighth abdominal tergite without an obtuse angle caudad of the slender 



downwardly projecting lateral process; hind femur without erect, soft 



hairs on posteroventral surface aequalis Malloch, 



Eighth adbominal tergite with an obtuse angle caudad of the process above 

 referred to — i. e., the process is indistinctly proximad of the posterior 

 lower angle (fig. 27) ; hind femur with fine, erect hairs on posteroventral 

 surface tenuispina Loew. 



25. Hind femur without a long fine hair close to apex on posteroventral surface; 



last abdominal sternite with two long tapering processes which are 



pointed at apices bispina Loew. 



Hind femur with one or more long fine hairs near apex on posteroventral 

 surface, sometimes the entire surface has a fringe of hairs ; apices of 

 processes of last sternite rounded 2t3 



26. The lateral extensions of last abdominal sternite much longer than third 



antennal segment 27 



The lateral extensions of last abdominal sternite not longer than third 

 antennal segment 28 



27. Hind femur with rather dense, long, fine hairs on its entire length ix»stero- 



ventrally ; the small spine at base of the slender inner hypopygial forceps 



long and simple (fig. 28) imitatrix Malloch. 



Hind femur with sparse fine hairs on posteroventral surface which do not 

 form a complete frings; the small spine at base of the slender inner 

 hypopygial forceps short, furcate (fig. 25) fratercula Mallocli. 



28. Seventh abdominal tergite with a group of short, black, setulose hairs at 



apex on each side; the fine, erect hairs on hind tibia confined to base! 



half seticauda Malloch. 



Seventh abdominal tergite without such hairs ; the fine, erect hairs on hind 

 tibia extending almost the entire length of anteroventral surface and 

 present on basal half of postero-ventral cllifera Malloch. 



29. Hind femur without a distinct preapical anteroventral bristle, 



inaequalis Malloch. 



Hind femur with a distinct preapical anteroventral bristle 80 



oO. Seventh abdominal tergite compressed, almost cylindrical ; cheek about or 

 quite half as high as eye; cross-veins usually as pale as the other 



veins 31 



Several abdominal tergite not compressed nor cylindrical ; cheek much 

 less than half as high as eye 32 



31. Hind trochanters with minute black hairs on ventral surface ; hairs on back 



of head and cheeks black littoralis Malloch. 



Hind trochanters with very few weak pale hairs on ventral surface : hairs 

 on lower half of back of head and cheek yellow, only the two bristles on 

 lower margin posteriorly black hartl Malloch. 



32. Prosternum with a few black hairs; penultimate section of fourth vein 



distinctly over half as long as ultimate bispina Loew. 



Pi-osternum bare 33 



33. Fore femur with two strong posteroventral bristles; cross-veins of wings 



noticeably darker than other veins tenuispina Loew. 



Fore femur with three or more posteroventral bristles ; cross-veins of winiis 

 almost imperceptibly darker than other veins seticauda Malloch. 



LIST OF SPECIES OF THE DISTRICT OF COLUMBIA REGION. 



S. aeqnalis Malloch.— Dead Run. Virginia, June 22. 1915, R. C. 

 Shannon. 



