AMERICAN DIPTERA. 391 



two taken together, of nearly equal width throughout; style a trifle 

 over one-half as long as the third segment. Palpi and proboscis black. 

 Thoracic dorsum more or less velvety black, showing only traces of 

 stripes; however, this is variable, as in one specimen there are two 

 rather ill-defined dark median stripes, separated by a grayish line 

 anteriorly, and abbreviated without coalescing behind the transverse 

 suture; the lateral and posterior margins of the dorsum, the scutellum 

 and the pleurae and the coxae, grayish-white pruinose, the pile of pleurae 

 and scutellum fine and white; the weak bristles before the hal teres, 

 on the sides of the dorsum and the two on the scutellar margin, yellow 

 (jr brownish. Abdomen polished bluish-black, sparsely clothed with 

 inconspicuous appressed yellowish hair above, and on the sides of 

 first two segments with longer white pile; the fifth and sixth segments 

 silvery-white pruinose, showing on their sides rather indistinctly two 

 short rows of two or three punctures each; lateral margins, especially 

 the anterior portion, of the segments, grayish pruinose; venter brown- 

 ish pruinose, spotted or streaked with white bloom. In shape the 

 abdomen is nearly of equal width to tip of the second segment; thence 

 evenly increasing in width to tip of the fifth; the sixth segment is 

 indistinctly narrower than the fifth, and from above wholly conceals 

 the small seventh and eighth segments and the hypopygium, which 

 are retracted more or less within it. The fifth segment is fully three 

 times as wide as long. Femora usually black, though sometimes 

 tinged with red; tibiae and tarsi reddish-brown with white or yellowish 

 hair and brownish bristles. Basal third of wings, except extreme 

 base, pure hyaline, the outer two-thirds blackish in varying degree, 

 darkest along the costa, on the veins at the bases of all the posterior 

 cells and at the furcation of the third longitudinal vein; on the costal 

 margin near the middle of the outer two- thirds there is usually a 

 hyaline spot. All the posterior and the submarginal cells open; anal 

 cell narrowly open or closed on the margin. The black of the wings 

 is variable and sometimes extends over into the basal third. 



9 . — Similar to male, but the abdomen not expanded distally; all 

 the segments on the lateral margins grayish pruinose; the fifth and 

 sixth segments without the silvery bloom present in the male. 



' Type. — Lost (Say) . The type of Pygostolus argeniifer is at 

 the M. C. Z. 



Habitat. — Atlantic States, being reported from Mass. (Osten 

 Sacken) ; Clementon (Apr. 15, C. W. Johnson), N. J. ; Pa. ; Md. ; 

 and Tifton (C. W. Johnson), Ga. 



Prof. C. W. Johnson says that this is a spring species, while 

 pictus appears in the fall of the year. 



TRANS. AM. ENT. SOC, XXXV. SEPTEMBER, 1909 



