332 ERNEST A. BACK 



or pile of mystax mostly confined to a dense row on the dome- 

 shaped oral margin, but sometimes extending upward on the 

 face. Eyes swollen in front, the fore part with much larger 

 facets; the facial and frontal orbits forming a distinct angle 

 with each other. Antennas (PI. Ill, fig. 9) short, approximate, 

 situated midway between the oral margin and the vertex: 

 first two segments short, subequal; third, elongate, tapering, 

 over one and one-half times the length of the first two taken 

 together; style, distinct, a little less in length than the first 

 two segments and composed of a long cylindrical basal seg- 

 ment, and a short bristle-like terminal appendage. Thoracic 

 dorsum somewhat flattened, usually with but two or three 

 distinct bristles on each side; one immediately before the 

 transverse suture, and one or two post alar. Trichostical pile 

 or bristles present. Abdomen rather elongate, flattened, with 

 bristles on the sides of the first segments; male genitalia ex- 

 tremely small and often retracted within the last segment. 

 Legs moderately robust, the femora sometimes quite robust 

 and swollen; the anterior tibiae without a terminal claw-like 

 spur. Wings normal; the submarginal and posterior cells 

 wide open, the anal cell closed a short distance before the 

 margin, the fourth posterior cell petiolate, sessile, or open at 

 its base. 



Type. — Dasypogon elegantulus Meigen. 



SYNOPSIS OF SPECIES. 



1. Scutellum with well-developed pile or bristles 2. 



Scutellum without noticeable pile or bristles 3. 



2. Head and thorax blackish; abdomen and legs sordid yellow; 



length 3 mm fragilis. 



Wholly black; everywhere silvery- white priiinose; length 6-8 mm. 



argenteus. 



3. Thoracic dorsum with anteriorly dilated geminate brown stripe, 



abdomen reddish abdominalis. 



Thoracic dorsum without a distinct geminate stripe; abdomen 

 black, trifasciate with white trifasciatus. 



Stichopogon abdominalis n. sp. 



(^ $. — Length cj\ 6.7-7.5 mm.; $, 8 mm. — -Head and thorax black; 

 wholly grayish-white pruinose except two larger spots on the vertex 

 confluent with the orbits and a moderately wide, anteriorly dilated, 



