c^ 



68 



vittjv; three postsutuial aiid two steinoplemiil niaciocli?ptoe; scutellum 

 beariug' three pairs of loii^" luargiual niaeioclia'tu'; abdoiiieu shiiiinj;-, 

 a i)air of iiiar^iual macroch;etio ou the (irst and second segments and 

 a marginal row on the third; genitalia projeetinjf at least twice the 

 length of the fourth abdominal seginent beyond tlie latter, curve<I 

 beneath the abdomen; lirst segment of abdomen in the female greatly 

 dilated veutrally; hind tibije not ciliate with bristles; front pul villi in 

 female one-half as long as, in the male about as long as, the last tarsal 

 joint; wings hyaline, a single bristle at base of the third vein, other 

 veins bare, api(;al cell open at the extreme tip of wing, bend of fourth 

 vein arcuate, hind crossvein nearly perpendicular, midway between the 

 snuill crossvein and bend of the fourth vein; calypteres white; length, 

 4 to 5 mm. Southern Illinois. Two males and one feniale collected by 

 ,-7 Charles liobertson. Type No. 3559, U. tS. National Museum, .atra n. sp. 



Genus LEUCOSTOMA Meig. 



Leucostoma Meigen, in Illiger's Magaziu fiir InsekteukuiHlc, Vol. II, p. 279; 1803. 



Clel'ut Desvoidy, Essai siu' les Myodaires, p. 2'x^; 1830. 



Psalida Rondani, Diiitciulogin' Italic^' rrodromuis, Vol. I, p. 70; 1856. 



This synonymy is given by Schiner' and repeated by Brauer and 



Bergenstamm.^ Our species are black, the pali>i sometimes yellow; 



three sternopleural and usually three postsutural macroch.eta^- : 



1. Thorax shining, almost destitute of pollen, frontal vitta at the 



lowest ocellus narrower than either side of the front at the same 



point, scutellum bearing three pairs of marginal macrocha^tie, 



first two segments of abdomen each bearing a marginal pair, 



l)alpi yellow li. 



Thorax opaque, densely gray pollinose, fnuital vitta of female at the 

 lowest ocellus twice as wide as either side of the front, paljn 

 black; front of female one and one-third times as wide as either 

 eye, two pairs of orbital bristles, cheeks one-sixth as wide as .the 

 eye-height, antenn;c two thirds as long as the face, the third 

 y joint as long as the second, arista thickened on the basal three- 

 p fifths, the penultimate joint shorter than broad; thorax not dis- 

 tinctly vittate, scutellum densely gray pollinose, bearing two 

 pairs of long marginal macrochnetie, abdomen shining, basal 

 half of the last three segments gray pollinose, first two segments 

 destitute of macrochu'ta', those of the other two segments very 

 short, genitalia of female daw-like, curved beneath the body; 

 wings hyaline, third vein bearing two or three bristles near the 

 base, hind crossvein straight, one and one-third times as long 

 as the last section of the third vein, situated midway between 

 the small crossvein and the bend; calypteres white; length, 

 5 mm. Clementon, N. J. A single female specimen collected 



' Fauna Austriaca, Vol. I, p. 542; 1862. 

 2Zweif. Kaia. Mus. Wieu, VI, Index; 1893. 



