NO. I BLACK FLIES OF GUATEMALA — DALMAT l8l 



and epicranial plates. Posterior sucker with 220-230 rows of hooks. 

 Anal gills composed of 3 main branches, each with 10 broad divisions, 

 rounded at their apices. The X-shaped sclerite is simple, anterior and 

 posterior arms well sclerotized, without pigmented patches except 

 between the two anterior arms at their union to each other. No rectal 

 scales or spines. No ventral papillae or plaques on eighth segment. 



Types. — Holotype (c^) and allotype ($), part on slides, the rest 

 on pins, and paratypes (15 (^(^ and $$, and pupae) in the collection 

 of the Instituto de Salubridad y Enfermedades Tropicales, Mexico 

 City; collected in Temixco, Morelos, Mexico, July 3, 1945. 



SIMULIUM (DYARELLA) MATHESONI Vargas * 



Simuliiim mathesoni Vargas, Rev. Inst. Salubr. Enferm. Trop., vol. 4, No. 4, pp. 



360-362, figs. 19-27, 1943 (original description, S and pupa). 

 Simulium (Dyarella) mathesoni Vargas, Vargas, Martinez, and Diaz, Rev. 



Inst. Salubr. Enferm. Trop., vol. 7, No. 3, p. 178, 1946 (larva). — Dalmat, 



Ann. Ent. Soc. Amer., vol. 44, No. i, pp. 55-57, 1951 (presence in 



Guatemala). 



Male (pi. 24, figs. 55-57)-— 4-5 mm. long. 



Head: Holoptic. Eyes reddish brown above, black below. An- 

 tenna 690 fx long, ii-segmented, slightly tapering, not blunt; segment 

 3>i-|-2, 3<4-f5, 3>ii; scape and pedicel light yellow, flagellum 

 dark brown. Palpi dark brown to black. Clypeus dark brown, with 

 white pruinosity and several long, tan hairs. 



Thorax : Mesonotum velvety black ; on either side of midline, 

 with its base on the anterior margin of mesonotum, is a white-pruinose 

 triangle, its apex extending posteriorly in the form of a white stripe 

 which blends with the pruinosity of prescutellar region ; few short 

 black hairs distributed on mesonotum and several long ones in prescu- 

 tellar region ; numerous rather long, slender, golden, scalelike hairs on 

 anterior half of mesonotum, along its lateral margins, and in prescu- 

 tellar region. Humeral angles white-pruinose. Pleura dark brown 

 to black, with white pruinosity. Scutellum black, with white pruinosity 

 and several long black hairs. Postnotum black, with white pruinosity, 

 but without hairs of any kind. Stem of halter brown, knob white. 

 Wings, 3.7 mm. long and 1.3 mm. wide ; relation of length of body to 

 wing, 1.2 : I ; Sc pilose along basal fifth ; Ri pilose on distal half; R2+3 

 pilose except for short basal section ; Cu2 arcuate ; discal cell absent. 



Legs: Leg i, length, 3.7 mm. ; coxa and trochanter yellow ; femur 

 yellow with black subapical patch ; tibia black with longitudinal yellow 

 patch in median area; tarsus black. Leg 2, length, 3.0 mm. ; coxa and 



* See footnote 6, p. 68. 



