290 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 90 



4. Each half of anal forceps (fig. 17, a) viewed in profile straight 



on posterior edge for six-sevenths of its length, then gently 

 curving inwardly and abruptly tapering to terminus— panaetius (Walker) 

 Each half of anal forceps (fig. 17, e) viewed in profile straight 

 on i)osterior edge for about one-half its length, then strongly 

 curved inwardly and tapering to a fine point apicata Curran 



5. Frontalia at middle of front about equal to or narrower than 



parafrontalia ; hairs of cheeks predominantly pale ; bristles of 

 facial ridges often weak and depressed ; face and front usually 



with a slight yellowish cast 6 



Frontalia at middle of front at least as wide as parafrontalia ; 

 hairs of cheeks predominantly black, comparatively long; 

 bristles of facial ridges strong and erect; face and front 

 silvery; a comparatively black, thinly gray-poll inose, western 

 species similis (Williston) 



6. Second genital segment orange-red 8 



Second genital segment black, usually reddish below 7 



7. Viewed from the side the anal forceps (fig. 17, f) strongly 



incurved, their posterior surfaces moderately to densely pilose 



and often obscured in outline acosta, new species 



Viewed from the side the anal forceps (fig. 17, 6) comparatively 

 straight, tapering abruptly to terminus, their posterior sur- 

 faces moderately pilose and distinct in outline nigricans, new species 



8. Parafacialia at narrowest part at least equal to if not wider 



than one-half distance between vibrissae ; second antenual 

 segment mostly reddish brown ; lobes of fifth sternite usually 

 smooth or with inconspicuous ridges on their inner edges- cana, new species 

 Parafacialia at narrowest part less than one-half distance 

 between vibrissae; second antennal segment mostly black; 

 lobes of fifth sternite usually with conspicuous ridges on 

 their inner edges variata Curran 



FEMALES 



1. Abdomen without discal macrochaetae 2 



Abdomen with discal macrochaetae dakotensis, new species 



2. Posterior border of fourth segment fringed with long bristles 



of unequal length 3 



Posterior border of fourth segment fringed with closely set, 

 short bristles of nearly equal length ; front wider than eye 

 and widening slowly to base of antennae apicata Curran 



3. Frontalia at middle of front narrower than parafrontalia, 



usually brownish ; hairs of cheeks predominantly pale 4 



Frontalia at middle of front at least as wide as parafrontalia, 

 usually black ; hairs of cheeks predominantly black, compara- 

 tively long; fourth abdominal segment black, mottled with 

 gray-poUinose areas; face and front silvery iX)lliuose without 

 yellowish cast; western species similis (Williston) 



4. Posterior preintraalar bristle well-developed; front widening 



slowly to base of antennae; cheeks about one-third the eye 



height; usually four dorsocentrals 5 



Posterior preintraalar bristle absent or vestigial ; usually three 



dorsocentrals 6 



