4 PEOCEEDINGS OF THE NATIONAL MUSEUM vol.76 



tional weak sublateral and small preapical pair present; postscu- 

 tellum small ; halteres yellow ; calypters white ; inf rasquamal setules 

 present. 



Abdomen rather slender, two basal segments either faintly or 

 pronounced yfellowish on the sides, otherwise black, subshining; 

 hairs on dorsum erect ;entirely covered with cinereous pollen which 

 is thinner on the narrow hind margins of the segments ; when viewed 

 from behind a narrow dorsal vitta present which becomes wider 

 basally; first segment with a row of weak marginals which may be 

 hairlike or incomplete above; intermediate segments each with a 

 complete marginal row, no true discal bristles present, although 

 the erect hairs often resemble discals on these segments; fourth 

 segment with a complete marginal and a discal row; venter with 

 long bristly hairs. Genitalia small, outer forceps broad lobelike 

 brownish black, inner forceps yellowish, slender, not divergent, tips 

 black; penis yellow basally, distal segment black, apex expanded in 

 a circular lobe with a narrow whitish border; fifth abdominal 

 sternite prominent, deflected downward, broadly incised, bearing 

 fine black hairs on the lateral margins. 



Legs yellow basally, tarsi black ; middle tibia with one short bristle 

 on outer front side distinctly beyond the middle ; claws and pulvilli 

 nearly as long as last tarsal joint. 



Wings subhyaline; veins yellow, third with two or three bristles 

 near base, all others bare; fourth vein broadly curved without a 

 definite angle or stump, nearly straight beyond bend; first posterior 

 cell narrowly open in the wing tip; hind cross vein perpendicular 

 to fourth vein, about equidistant from bend and small cross vein; 

 last section of fifth vein very short, hardly one-fifth the preceding 

 section ; costal spine present, usually prominent and doubled. 



Female.— Front 0.32 of head width (average of six, 0.33, 0.30, 0.33, 

 0.31, 0.35, 0.33) ; inner orbits parallel from vertex to base of anten- 

 nae; vitta brown, about one-half the width of paraf rentals, which 

 are thinly gray pollinose reflecting blackish above; the usual two 

 pairs orbitals present; the uppermost f rentals large and directed 

 posteriorly outward; outer verticals about one-half as long as the 

 inner ones ; antennae, thorax, scutellum, and abdomen more yellowish 

 and wings broader than in male. Genital segments as in ohscura. 



Length : Male, 5 to 6.5 mm. ; female, 4.5 to 6.5 mm. 



Described from 10 males and 8 females, all collected at College 

 Station, Tex., March to June, 1919-1928 (H. J. Keinhard). 



Type. — Male, Cat. No. 41985, U.S.N.M. Four paratypes, including 

 both sexes, also deposited in the National Museum. 



This species is very closely allied to the genotype obscura, from 

 which it differs in the vety narrow front of the male, the yellow ab- 



