4 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



third joint distinctly broader than the basal joints and somewhat pointed; 

 arista moderate, pubescent. Front cupreous metallic green. Postocular 

 cilia delicate, black above, light yellow below. Thorax shining except 

 anteriorly where it is covered with yellow dust. The dust runs back in two 

 broad bands leaving a narrow shining streak in the mid-dorsal line. Abdo- 

 men slightly compressed dorsoventrally at its base, covered with short black 

 hairs and with a layer of white dust along the sides. Hypopygium black 

 with bronze green reflections and a layer of white dust. !, Lamellae triangular, 

 yellow, bordered with black and with a fringe of delicate, black hairs. Pleurae 

 metallic green covered with a layer of white dust. Coxae of the same color 

 except the fore pair, which are yellow. These have short white hairs on 

 their anterior surfaces and a few black bristles near their apices. Legs yel- 

 low, trochanters with a small black spot on their posterior faces. Tarsi 

 blackened from the tip of the first joint. First joint of middle tarsi rather 

 slender, white; second, third and fourth joints distinctly compressed from 

 side to side and fringed with black hairs. Hind tibiae somewhat thickened, 

 with black tips. Wings not broadened, grayish hyaline, distinctly yellowish 

 towards the costa, which bears a slight swelling at the junction of the humeral 

 vein. The anal angle is distinctly bilobed and prominent. Distal segment 

 of fourth vein with a decided angle but without traces of a stump-vein. It 

 ends some distance before the apex of the wing. There is a small but dis- 

 tinct notch in the hind margin at the tip of the fifth vein. Halteres and teg- 

 ulse yellow, the latter with long black cilia. 



Female. Length 4-5-5-5 mm.; length of wing 4-5-5-5 mm. Face broader 

 than that of the male, with grayish yellow dust. Anal angle of wing not 

 bilobed, the costa without the swelling at the junction of the humeral vein. 

 Middle tarsi very slightly compressed. Cilia of the tegulae black, nearly as 

 long as in the male. Appendages of the ovipositor yellow with black tips. 



Numerous specimens, mostly males, collected by J. M. 

 Aldrich at Moscow, Idaho. I have also taken several spec- 

 imens, mostly females, in sweepings along the water-courses 

 in western Wyoming in September (Dubois, Two-gwo- 

 te-ee Pass). 



In having laterally compressed middle tarsi the male of 

 H. Aldrichii resembles the male of H . lati^es, but the com- 

 pression in the western is not so great as it is in the eastern 

 species. In latifes the hind tibise are yellow throughout, 

 in Aldrichii distinctly tipped with black; the anal angle of 

 the wing in the male of the former species is evenly rounded, 

 in the male of the latter, bilobed and prominent; the base 

 of the second middle tarsal joint is yellow in latipes, entirely 

 black in Aldrichii. Lastly, the antennge of Aldrichii are 

 blacker and more hairy than those of the eastern species. 



