292 ERNEST A. BACK. 



length of the first two taken together, narrow, almost linear; the style 

 is very short, perhaps one-tenth of the length of the segment, cylin- 

 drical, with a minute bristle; ocellar tubercle rather large and broad, 

 with deep grooves on each side between it and the orbit of the eye; 

 both the tubercle and the opposite side of the groove are beset with 

 black pile, which commonly form a distinct tuft on the top of the 

 head; on each side of this tuft, along the orbits of the eye, there is a 

 narrow margin of minute microscopic yellowish-white hairs; lower 

 down, on the orbit, on a level with the antennas, there is, on each side, 

 a small tubercle, the upper and outer side of which is clothed with the 

 same microscopic yellowish- white pile; the occiput is beset with white 

 hairs, except in its upper part, where there are some black hairs. 

 Thorax black, clothed with a thin gray bloom; three indistinct stripes 

 are somewhat brownish; the lateral ones are incurved and somewhat 

 expanded anteriorly, where they end in a brown spot above the hu- 

 merus; the median 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 

 fiat, 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, polished, moderately convex, of nearly equal 

 breadth; segments 2-6 anteriorly have a narrow cross-band of white 

 bloom, not reaching the lateral margins; on that margin, in the pos- 

 terior angles of each of the same segments, there is a large white spot. 

 The two basal segments 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 tibiae gradually in- 

 crassated from the base to the tip; the first segment of hind tarsi also 

 somewhat stout. Halteres pale brownish. Wings hyaline; venation 

 normal." 



Type. — M. C. Z. Six male and six female specimens. 



Habitat. — Los Guilucos, Sonoma Co., Cal. (Osten Sacken, 

 July 5, 1877). 



" This species differs in many respects from the typical one 

 of the genus. The broad ocellar tubercle with the deep 

 grooves on each side of the antennas, the row of erect bristles 

 on the lateral stripes of the thoracic dorsum, the subclavate 

 hind tibiae, the shortness of the antennal style in proportion 

 to the length of the third segment, the gently convex but 

 hardly gibbose face, the conspicuous six bristles on the other- 

 wise bare scutellum, are so many characters which are not 

 found in other species." 



