84 DIPTEEA OF NORTH AMERICA. [PART II. 



barbatulus by its larger size, its longer and darker wings, and by 

 a darker and less hairy face ; the male further differs by the greater 

 length of the lamellae of the hypopygium. From G. scotias it dif- 

 fers by the third joint of the antennas, which has not the long hairs, 

 so apparent in G. scotias. 



Observation 2. A male from the same locality shows a con- 

 siderably stronger convergency of the third and fourth longitudinal 

 veins, coincides, however, so much in all the other characters with 

 the rest of the males, that I cannot consider it for more than a 

 variety, although a very striking one, of G. tristis. 



B. Prevailing color of the feet yellow. 



6. G. exilis LOEW. . Viridis, pedibus flavis, coxarum intermedia- 

 rum basi femorumque posticorurn apice nigricantibus, tarsis fuscis. 



Green, with, yellow feet, the basis of the middle coxae and the tip of the 

 hind femora blackish, tarsi brown. Long. corp. 0.10. Long. al. 0.11. 



SYN. Gymnopternus exilis LOEW, Neue Beitr. VIII, 30, 5. 



Green or 'bluish-green, not very bright. Face and front light 

 grayish. Antennae brownish-black ; the second joint and the root 

 of the third reddish-brown ; the third joint comparatively rather 

 large, not very broad in proportion to its size, not rounded at the 

 tip, distinctly hairy ; the pubescence of the not very long arista 

 is difficult to perceive. Cilia of the inferior orbit black. Tho- 

 rax, in consequence of a light cover of dust, somewhat dull, and 

 grayish-green. In one specimen only, I perceive upon the 

 scutellum, besides the usual bristles, a few small hairs, which are 

 rather indistinct. Feet pale yellowish. Middle coxes upon the 

 outside distinctly blackened beyond their middle. Hind coxse 

 darkened only at the basis. Tip of the hind femora distinctly 

 blackened upon the upper side. Fore and middle tarsi infuscated 

 from the tip of the first joint; hind tarsi black-brown to the same 

 extent. The row of short small bristles which is usually found 

 upon the upper side of the fore tibiae in the species of Gymnop- 

 ternus is less developed here than in most of the other species. 

 Cilia of the tegulae black. Wings gray. The small lamellae of the 

 hypopygium yellow, fringed with rather apparent, small black 

 bristles ; their form is rather kidney-shaped, still they have in the 

 lower corner a very small, somewhat protruding black flap ; the 



