NO. I BLACK FLIES OF GUATEMALA — DALMAT I77 



Thorax : Mesonotum shiny rust brown, covered with white prui- 

 nosity except for i median and 2 lateral longitudinal lines which show 

 the base color ; black hairs over entire mesonotum, somewhat longer 

 on prescutellar region; yellow scalelike hairs all around periphery of 

 mesonotum, in small groups along the anterior margin. Humeral 

 angles dark brown with gray pruinosity. Pleura dark brown, with 

 light pruinosity. Scutellum shiny rust brown, with few black hairs on 

 either side. Postnotum shiny rust brown, without hairs. Stem of 

 halter dark brown and hairy, the knob tan. Wings, 3.8 mm. long and 

 1.6 mm. wide; relation of body length to wing, i.i : i ; Sc pilose on 

 basal third ; Ri with hairs and spines on distal half ; R2+3 pilose on 

 distal three-fourths ; Cuo arcuate ; discal cell absent. 



Legs: Leg i, length, 4.1 mm.; coxa, trochanter, and femur tan; 

 tibia and tarsus dark brown. Leg 2, length, 3.4 mm. ; coxa dark 

 brown ; trochanter tan ; basal two-thirds of femur light brown, apical 

 third dark brown ; basal halves of tibia and basitarsus light brown, 

 apical halves dark ; second through fifth tarsal joints black. Leg 3, 

 length, 4.2 mm. ; coxa brown, trochanter light brown ; femur dark 

 brown with basal light ring ; tibia dark brown ; basal halves of basi- 

 tarsus and second segment tan, the remainder dark brown to black ; 

 tarsal segments 3 through 5 black ; relation of basitarsus to second 

 joint, 2:1; calcipala well developed, straight and wide, almost reaching 

 pedisulcus ; pedisulcus well developed, deep, on basal third of second 

 segment. 



Abdomen : Anterior half of first tergite brown, posterior half 

 black; pleura of this segment with black anterior half, the posterior 

 half white-pruinose, clothed with long brown hairs that reach the 

 fourth segment. Remaining segments velvety black, the pleura white- 

 pruinose, invested with short black hairs. Sternites tan, with dark- 

 brown region along midline. 



Genitalia: Sidepiece (pi. 24, fig. 52) irregularly quadrangular in 

 shape, its outer margin 1.5 times as long as the inner margin; some- 

 what wider than long ; dorsal opening large, approximating the con- 

 tour of the sidepiece. Clasper (pi. 24, fig. 52) slightly more than 

 twice as long as wide, sinuous, with long bulge near distal end of 

 outer margin and smaller bulge near base of inner margin ; well- 

 marked opening at base ; narrower than rest of clasper, rounded ; 

 terminal spine single, near edge of clasper. Both sidepiece and clasper 

 with numerous long, stout, spinelike hairs. Body of adminiculum 

 (pi. 24, fig. 53) irregularly quadrangular, its width about 1.5 times 

 its length, the apex with depression ; on ventral surface of adminicu- 

 lum, passing longitudinally along midline, is a very low keel, tent- 



