126 DIPTERA OP NORTH AMERICA. [PART II. 



serted black hairs of 'greater length than those on the under side 

 of the hind femora, which are brownish-black at the tip. Tibia? 

 moderately provided with bristles, the hind tibiae blackened at the 

 tip. Fore tarsi towards the end only slightly infuscated ; the first 

 joint is at least 1^ the length of the four following joints together, 

 upon the under side with a row of delicate, but rather long little 

 hairs, which may be easily overlooked. Middle tarsi from the 

 tip of the first joint blackish-brown ; however, the root of the next 

 following joints somewhat paler ; the first joint is at least by one- 

 third longer, than the following four joints together. Hind tarsi 

 entirely black, first and second joint of about the same length, 

 the following of a decreasing length. Cilia of the tegulse, which 

 have a black margin, yellowish-white. Wings somewhat grayish 

 with blackish-brown veins ; the last segment of the fourth longitu- 

 dinal vein is strongly bent forward before its middle. 



Female. Face broader than that of the male, and the palpi 

 much larger, the latter with a distinct covering of white dust. 

 The third joint of the antenna?, as usual, much smaller than that of 

 the male. The dust upon the thorax and the scutellum less thick, 

 so that the green ground -color is distinctly visible in every direction. 

 The ground-color of the abdomen is shining and metallic-green, 

 the dust upon it is confined to the anterior half of the segments, 

 extending only upon the last segment as far as the posterior mar- 

 gin ; the yellow spots of the second segment are about of the same 

 size and nature as those of the male, those of the third segment 

 occupy only the anterior corners and are much smaller. The 

 hairs upon the under side of all the femora are short and the hind 

 femora are very slightly infuscated at the tip only. All the rest 

 as in the male. 



Hab. District Columbia. (Osten-Sacken.) 



Observation 1. — Notwithstanding the difference in the coloring 

 of the hind femora, the female agrees with the above described 

 male so much, that I cannot have the least doubt of its being the 

 other sex of Argyra albicans. 



Observation 2. — Argyra albicans can easily be distinguished 

 from the European Argyra diaphana by its somewhat smaller 

 size, the paler color of its fore coxa? and of the cilia of the tegulas. 

 Nevertheless it resembles it very much. As Fabricius, in his 

 Systema Antliatorum, states America to be the home of his Musca 

 diaphana, it might well be supposed that he meant Argyra albi- 



