1921] NATURAL SCIENCES OF PHILADELPHIA. 57 



femora and tibiae broadly tipped with black; wings faintly grayish, 

 the costal region slightly infuscated; wing-base conspicuously pale; 

 distal section of Ri longer than Rs. 



Male. — Length about 5.5 mm. ; wing 5.7 mm. 

 Female. — Length about 7 mm.; Aving 6.4 mm. 



Rostrum and palpi dark l^roAvn. Antennal scape dark brown, 

 the flagellum broken. Head gray, clearer and lighter gray adjoin- 

 ing the inner margins of the eyes. Mesonotum gray pruinose, 

 the median area broadly brownish, the extreme lateral margins 

 narrowly whitish; remainder of the mesonotum brown, sparsely 

 dusted with grey. Pleura brown, darker dorsally; sternum dark 

 brown, paler medially beneath. Halteres pale. Legs with the 

 coxae brownish testaceous; trochanters similar, the margin with a 

 black spot; anterior femora whitish, the tips broadly and conspicu- 

 ously blackened and with an indistinct whitish subterminal ring; 

 posterior femora brown, gradually darkening to the black tips; 

 tibiae white, the tips broadly and abruptly black ; tarsi white. Wings 

 with a faint greyish tinge, more brownish in the costal region ; wing- 

 base before the arculus conspicuously whitish; veins pale brown. 

 Venation: Sc moderately long, Sci ending opposite about three- 

 fourths the length of Rs, Sco rather indistinct, at the tip of Scu 

 Rs long, strongly arcuated at origin; r about mid-distance between 

 Se2 and the tip of Ri, the distal section of Ri being a little longer 

 than Rs; r-m shorter than the basal deflection of Mi + 2; petiole 

 of cell Mi longer than vein Ma," basal deflection of Cui about its 

 own length before the fork of M. Abdominal tergites dark brown, 

 the sternites a little paler. 



Habitat. — Peru. 



Holotype, o^, Yurimaguas, April 8, 1920 (H. S. Parish). 



Allotopotype, 9 , April 1, 1920. 



Paratopotype, Sex ?, April 5, 1920. 



Orimarga pallidibasis is readily told from the other known spe- 

 cies of the genus by the position of the radial cross vein, vein Ri 

 beyond it being a little longer than the sector; in most species of the 

 genus, r lies close to the tip of Ri. 



Genus DIOTREPHA Osten Sacken. 



1878. Diotrepha Osten Sacken, Cat. N. Amer. Dipt., p. 219. 

 1888. Thambeta Williston, Synopsis N. Am. Dipt., p. 32. 



Diotrepha atribasis Alexander. 



1914. Diotrepha atribasis Alexander, Trans. Am. Ent. Soc, vol. 40, p. 240. 



Flores, Brazil, November 18, 1919 (H. S. Parish). 

 Teffe, Brazil, December 22-24, 1919 (H. S. Parish). 

 Iquitos, Peru, June 7, 1920 (H. S. Parish). 



