1919] Hine: Genus Erax 131 



species than others. Ten species of this group are at hand and at least 

 one other is characterized sufficiently so that it should be determined 

 easily when specimens are procured. 



1. Vestiture of the scutellum, aside from the black marginal bristles, black or 



yellow 2 



Vestiture of the scutellum, aside from the black marginal bristles, white. . . .4 



2. Vestiture of the scutellum black jubatus Williston 



Vestiture of the scutellum composed of black bristles on the margin and yellow 



hair on the disc ". . . . .3 



3. Male with the last four abdominal segments silvery concinnatus Williston 



Male with the last two abdominal segments silvery carinatus Bellardi 



4. Femora red apically and sometimes posteriorly ,5 



Femora all black fi 



. Second to fifth abdominal segments of the male with long white hair parted 

 at the middle and directed outward, abdomen wholly gray poUinose. 



unicolor Bellardi 



Abdomen without hair parted at the middle and directed outward, basal 



segments of the abdomen black parvulus Bellardi 



6. Robust species, mane-like crest of the anterior part of the mesothorax, 



especially thick and long, male costa very prominently thickened, 



subcupreus Schaeffer 

 Slender species, mane-like crest normal, male costa only slightly thickened. . .7 



7. Male abdomen with only the last two or three segments entirely silvery, 



without prominent white hair parted at the middle and directed" outward; 



other segments with black markings latrunculus Williston 



Male abdomen with at least four or five segments silvery, and with long white 

 hair parted at the middle and directed outward 8 



8. Hypopygium divided apically with both parts of nearly equal length. 



cressoni n. sp. 



Hypopygium emarginate apically with the upper part much shorter than the 



lower costalis Williston 



Erax carinatus Bellardi. 



Total length 18 millimeters. Body yellowish gray pollinose, hairs 

 and bristles black and pale yellow. Mystax yellow with a few black 

 bristles, beard paler yellow than the mystax, ocellar bristles black, 

 hair on scutellum and in front of it straw yellow, a few black bristles 

 on the scutellar margin; femora black, tibise and tarsi largely red, 

 bristles black. Abdomen with short, sparse, j^ellowish hair, segments 

 six and seven silvery. See Figure 58. 



Male from Guerrero, Mexico. 



Erax concinnatus Williston. 



Total length 16 millimeters. Mystax and beard pale yellow, the 

 former mixed with black bristles, palpi black haired. Disc of scutellum 

 and rear of mesothorax yellow haired, margin of scutellum with a few 

 black bristles. Femora entirely black, tibiae and tarsi yellow, apex of 

 tibia and each tarsus darker. Wings yellowish hyaline. Abdominal 

 segment one and two and base of three black dorsally, sides of first 

 three segments, apex of three and all of four to seven inclusive, silvery, 

 hypopygiiun black, of medium size. See Figure 57. 



Male from Guerrero, Mexico. 



