OSTEN SACKEN ON WESTERN DIPTERA. 309 



in its upper part, where there are some black hair?. Thorax black, 

 clothed with a thin, gray pollen ; three indistinct stripes are somewhat 

 brownish; the lateral ones are incurved and somewhat expanded ante- 

 riorly, where they end in a brown spot above the humerus; the me- 

 dian line is simple and rather indistinct ; the dorsum is clothed with 

 short, sparse, white pile and longer black bristles; some of the latter 

 form two' rows on the lateral thoracic stripes. Scutellum flat, with six 

 black, conspicuous, erect bristles on its hind edge. The fan-like fringe of 

 hairs in front of the halteres is usually mixed of black and white hairs, 

 its upper part being black, the lower one showing some white hairs ; in 

 some specimens, principally males, it is altogether white. Abdomen 

 black, shining, moderately convex, of nearly equal breadth ; segments 

 2-6 anteriorly have a narrow cross-band of white pollen, not reaching 

 the lateral margin ; on that margin, in the posterior angles of each of 

 the same segments, there is a large white spot. The two basal seg- 

 ments have some long white hairs on the sides. Legs black, densely 

 clothed with short appressed white pile, beset with longer white hairs 

 and black bristles; hind tibi» gradually in crassated from the base to 

 the tip; first joint of hind tarsi also somewhat stout. Halteres pale 

 brow^nish. Wings hyaline ; venation normal. 



Hal). — Los Guilucos, Sonoma County, July 5. Three males and five 

 females. 



This species differs in many respects from the typical ones of the 

 genus. The broad ocellar tubercle with the deep grooves on each side, 

 the peculiar tubercles near the eyes on each side of the antennae, the 

 row of erect bristles on the lateral stripes of the thoracic dorsum, the 

 subclavate hind tibise, the shortness of the antennal style in proportion 

 to the length of the third joint, the gently convex but hardly gibbose 

 face, the conspicuous six bristles on the otherwise bare scutellum, are 

 so many characters which are not found in the other species. 



Half a dozen specimens, taken in Mariposa County and Yosemite 

 Valley (June 3-13), resemble G. cerussatus in having the white stripes 

 on the anterior margins of the thorax ; but they have no tubercles near 

 the eyes, and are abundantly distinct in many ways. The specimens 

 being injured, I abstain from describing the species. 



18. Cyrtopogon nebulo n. sp., $ .—Gray ; thorax with a geminate 

 brown stripe ; abdomen shining black, with white spots in the hind cor- 

 ners of segments 1-5; wings with brown clouds on the cross- veins and 

 on the bifurcation of the third vein. Length 8-9™". 



Face and front grayish-pollinose, with black hairs ; the hairs on the 

 face, in a certain light, look whitish at the tip ; occiput with white hairs. 

 Antennoi black. Thorax grayish-pollinose, with brown stripes ; the in- 

 termediate one dark brown, geminate, abbreviated before reaching the 

 scutellum, but coming in contact with a pair of elongated brown spots 

 in front of the scutellum ; scutellum convex, with rather dense, long, 

 and soft white hair, and some blackish bristles along the hind edge? 



