352 ERNEST A. BACK. 



hal teres yellowish. Abdomen polished; segment 1, especially on the 

 sides, and the posterior lateral margins of segments 2-5, whitish 

 pruinose. Wings hyaline; fourth posterior and anal cells open, in 

 the female the basal segments of the abdomen, the entire legs, the 

 palpi, and often the antennae are reddish, and the thoracic dorsum, 

 upper pleurae and scutellum more brassy-yellow pruinose, while the 

 lower pleurae and coxae are whitish pruinose. 



Type.—U. S. N. M., Cat. No, 7960. The two co-types of 

 albifrons, the description of which was in press at the time 

 of the publication of semiustus, are at the University of 

 Kansas. 



Habitat. — San Diego, Cal. (type, Coquillett) ; Bill Williams 

 Fork, Ariz. (F. H. Snow, Aug.). 



This species is similar in form to combustus and dispar, 

 though not as robust. It will be easily separated from hya- 

 linus, which it most closely resembles, by its smaller size and 

 the dense grayish bloom of the head and thoracic dorsum, 

 which is in sharp contrast to the reddish abdomen. In 

 hyalinus the thoracic dorsum is a darker, — a yellowish-brown 

 pruinose. 



DEROMYIA. 

 Deromyia Phillippi, Verh. Zool.-Bot. Ges., XV, 705, 1865. 

 Deromyia Schiner, Verh. Zool.-Bot. Ges., XVI, 653, 1866. 

 Diogmites Loew, Cent., VII, 36, 1866. 



Deromyia Van der Wulp, Tijdsch. V. Ent., XXV, 92, 1882. 

 Deromyia Williston, Trans. Am. Ent. Soc, XI, 23, 1884; 



Psyche, 1889, 256; Biologia, Dipt., I, 310, 1901. 

 Diognites Osten Sacken, Biologia, Dipt., I, 173, 1887. 



Species of moderate to large size with elongate bodies ; front 

 tibiae with a claw-like spur. Head broader than high, disc- 

 iform; face broad, bare (sometimes with inconspicuous hair), 

 with bristles on the oral margin, in profile straight or slightly 

 concave, the oral margin most prominent. Antennae (PI. Ill, 

 fig. 10) of moderate length, first two segments subcylindrical, 

 the second longer than the first, both with bristly hair; third 

 segment as long as the first two taken together, fusiform, bear- 

 ing on its depressed distal end a short spine-like style, clothed 

 above on the basal half with stiff, forward directed, appressed 

 hair. Front but little wider than face, not widened above; 

 vertex but little depressed; ocellar tubercle with two long 

 bristles; occiput with well-developed bristles. Thorax only 



