2^6 DIPTERA OF NORTH AMERICA. [PART II. 



length. The opaque thorax, dusted with grayish, has two longi- 

 tudinal lines, distant from each other upon the middle, and two 

 other incomplete longitudinal lines of a brown color, occupying 

 the place of the lateral stripes. Bristles of the thorax proportion- 

 ally short. Seutellum with two bristles. The abdomen, dusted 

 with grayish and rather opaque, has upon the second segment a 

 large blackish, triangular spot, with its point directed backwards ; 

 upon each of the following segments there is a similar spot, which 

 is connected with the rather narrow black anterior margin of the 

 segment, and the color of which is changing from a dusky-bronze 

 into grayish-green. The structure of the hypopygium and of its 

 appendages is nearly as in P. albifrons Meig. ; the external 

 appendages are hardly half so long as the inner ones and have 

 the form of a small elliptical lamella ; their color is brown, their 

 pubescence near the basis more delicate, shorter and pale, at the 

 tip coarser, longer, and black ; the inner appendages form a 

 brownish-yellow forceps, dark-brown at the tip. Coxae and feet 

 yellowish, still the middle and hind coxa? rather broadly infuscated. 

 Fore coxa? beset only with a delicate, moderately long, yellowish- 

 white pubescence, without stouter bristles. All femora slender, 

 upon the under side very glabrous ; the few pale hairs which are 

 to be found there are extremely short, and therefore hardly per- 

 ceptible. Pubescence of all the tibia? very short, that of the 

 middle tibia? somewhat longer and more diverging. Fore tibia? 

 upon the upper side with a few slender minute bristles, one of 

 which is inserted at their tip. Middle tibia? generally infuscated 

 upon the two last thirds of their upper side ; upon their ante- 

 rior side, not far from the basis, a more perceptible small black 

 bristle is inserted ; otherwise they are without bristles. Hind 

 tibia? with a few very small bristles at the tip, otherwise as good 

 as without bristles. Fore tarsi slender, double the length of the 

 tibia? ; their first joint somewhat longer than the tibia ; the three 

 following joints of nearly the same length ; the fourth joint some- 

 what flattened from the sides, whitish ; fifth joint only about half 

 as long as the fourth, dark-brown. Middle tarsi once and a half 

 the length of the tibia?, slender; the first joint distinctly longer 

 than the following taken together ; the latter of a decreasing 

 length, the last one infuscated. Hind tarsi somewhat shorter 

 than the tibia?, their first joint distinctly shorter than the second, 

 the last one somewhat infuscated. Halteres yellowish ; tegula? with 



