216 DIPTERA OF NORTH AMERICA. [PART IV. 



slender towards the tip. Thorax reddish-yellow, shining above, 

 sometimes with a faint longitudinal brown line in the middle ; 

 pleurag paler yellow, with a hardly perceptible yellowish bloom, 

 which is also perceptible beyond the suture above ; halteres with 

 a more or less infuscated knob. The auxiliary vein is nearly 

 opposite the inner end of the second submarginal cell ; its tip has 

 the appearance of being incurved towards the first longitudinal 

 vein, wliereas the cross-vein seems to be placed between it and 

 the costa ; the pra^furca is arcuated at its origin, and remarkably 

 short, not longer than one-third of the length of the second sub- 

 marginal cell ; petiole of the first submarginal cell of moderate 

 length, sometimes but little longer than the small cross-vein, some- 

 times about the length of the great cross-vein ; first submarginal 

 ceil gradually tapering towards its inner end ; second submarginal 

 cell a little longer than the first posterior ; marginal cross-vein at 

 the tip of the first longitudinal vein, and not far from the middle 

 of the anterior branch of the second vein ; great cross-vein usually 

 about the middle of the discal cell : seventh longitudinal vein 

 slightly sinuated in the middle, and somewhat curved in the 

 opposite sense at the tip. The tip of the wing, between the 

 stigma and the apex, is more or less distinctly clouded with 

 brown along the margin. The ovipositor of the female is moder- 

 ately long, slender, perceptibly arcuated. 



The specimens vary in the following characters : — 



The larger specimens have a yellowish abdomen, brownish 

 along the lateral margins only ; the feet are yellowish ; femora 

 with a distinct brown band before the tip ; tip of the tibiae brown ; 

 wings with a yellowish tinge ; stigma dark brown ; a narrow 

 brown cloud runs along the fifth longitudinal vein and the central 

 cross-veins ; a brown mark at the origin of the prrefurca ; the 

 cloud at the tip of the wing is dark and very well marked. 



A series of smaller specimens have a brownish abdomen, and 

 brownish-tawny feet, except the coxse and the basis of the femoi'a, 

 which are pale ; the wings have a very pale tinge, and have no 

 clouds, except the more or less faint apical cloud and the more 

 or less infuscated stigma ; the latter is sometimes quite pale. 



Between these extremes, gradations in size and coloring occur, 

 which compel the describer to unite all these forms into one 

 species, until further observation brings more light upon the 

 subject. 



