206 DIPTERA OF NORTH AMERICA. [PART II. 



femora of a plain structure, not stouter than the middle femora ; 

 their under side has only close before the tip, a few black bristles. 

 The comparatively stout fore tibiae have on their front side, not 

 far from their basis, a stout black thorn ; their tip is elongated into 

 a very stout tooth, before which the under side of the tibiae, which 

 is beset with strong bristles, has a small excision. Middle tibia? 

 not quite so long and slender as those of S. exustus, on the upper 

 side only with three or four short bristles, on the under side with 

 a row of extremely long, straight, erect black bristles, and on the 

 hind side with long curved hairs, which latter are more dense near 

 the tip and curl up to the shape of a lock of hair. Hind tibiae 

 plain, scarcely stouter than the middle tibiae ; on their upper side, 

 not far from the basis, there is a strong bristle, and on the latter 

 half a few small bristles ; the under side is beset with short small 

 bristles, which are isolated upon the first part and closer together 

 and in more regular order upon the second half; at the end of the 

 under side there is a considerable number of less strong and less 

 short bristles, of which the last is distinguished by its greater 

 length ; on the outside of the tip of the tibiae there are several 

 short and one longer and curved bristle, which has almost the 

 thickness of a thorn. Tarsi plain, the joints of decreasing length, 

 the first joint of the fore and of the middle tarsi with more, that 

 of the hind tarsi with less bristles. Halteres yellowish-brown, the 

 lower part of the. knob more dark. The wings of uniform breadth 

 and at the end more rounded than in the other species ; an un- 

 commonly large black spot covers their apical half with the excep- 

 tion of a broad gray border on the posterior margin, and extends 

 as a broad cloud along the fifth longitudinal vein almost as far as 

 the anal cell ; inside of the discoidal cell it is somewhat paler, 

 otherwise, however, so dark that the two black spots, peculiar to 

 this genus, upon the posterior transverse vein and upon the last 

 segment of the fourth longitudinal vein, can only be perceived 

 when the wing is held towards the light ; the anterior part of the 

 wing from the basis as far as the middle is dingy-whitish hyaline ; 

 the anal angle and a broad border along the posterior margin are 

 more hyaline-gray. 



Hob. Port Resolution, Hudson's Bay Territory. (Kennicott.) 



Female. It is distinguished from the male by the following 



characters : Face with pale yellow-grayish, front with brown dust. 



The middle of the upper side of the thorax with yellow-brownish 



