NO. I BLACK FLIES OF GUATEMALA — DALMAT 235 



Thorax : Mesonotum velvety black ; with continuous band of white 

 pruinosity around the periphery, the anterior arm indented toward the 

 center of scutum along its midregion ; quite long, narrow, yellow, 

 scalelike hairs on entire mesonotum, more numerous around periphery 

 and on anterior fourth and in the prescutellar region, never in packets ; 

 entire scutum clothed with short black hairs, the hairs being longer and 

 heavier in the prescutellar region. Humeral angles black, with white 

 pruinosity and yellow scalelike hairs. Scutellum black, with yellow 

 scalelike hairs and long black hairs. Postnotum velvety black, com- 

 pletely white-pruinose, devoid of hairs. Pleura black, with white 

 pruinosity; pre-alar cluster yellow. Stem of halter black, the knob 

 yellow. Wings, 3.4 mm. long and 1.6 mm. wide; relation of body 

 length to wing, i : i ; Sc pilose along basal fifth ; Ri pilose and spiny 

 along distal half; R2+3 pilose except for basal seventh; Cu2 arcuate; 

 discal cell absent. 



Legs: Leg i, length, 3.4 mm. ; coxa, trochanter, and femur black; 

 tibia black, the median half of its anterior face tan ; tarsus black. Leg 

 2, length, 3.1 mm. ; coxa, trochanter, and femur black ; tibia black with 

 tan basal ring ; basal third of basitarsus tan, apical two-thirds black ; 

 segments 2-5 black. Leg 3, length, 4.0 mm.; coxa, trochanter, and 

 femur black ; tibia black with tan basal ring ; basal two-fifths of basi- 

 tarsus and basal third of second segment tan, the remainder of these 

 segments, as well as all of tarsal segments 3-5, black ; relation of basi- 

 tarsus to second segment, 5:1; calcipala well developed, reaching 

 pedisulcus ; pedisulcus well formed one-third the distance from the 

 base of second segment. 



Abdomen: Tergite of segment i black with short black hairs; 

 pleurites black with long black hairs that reach segment 4. Segment 2 

 black, the anterior half white-pruinose, with short black hairs. Other 

 segments black, part of pleural regions white-pruinose, with lateral 

 tufts of long black hairs as well as short black ones over entire seg- 

 ment. Sternites dark brown, with some white pruinosity. 



Genitalia: Sidepiece (pi. 26, fig. 91) wider than long, almost 

 oval in shape, with dorsal depression near middle of apical margin ; 

 dorsal opening occupying more than half of dorsal surface of side- 

 piece, its margins also somewhat rounded. Clasper (pi. 26, fig. 91) 

 longer than sidepiece, not very wide, of about equal width throughout, 

 the apex not narrowed but truncate, with single terminal spine ; very 

 short, broad basal process. Adminiculum (pi. 26, fig. 92) with charac- 

 teristic X-shaped appearance, the body trapezoidal and the basal 

 processes long and divergent ; lateral margins more hyaline ; apical 

 angles somewhat prolonged ; with well-sclerotized ribbonlike structure 



