May, 1920] Descriptions of Diptera 275 



12a. Fifth abdominal stemite with a pair of contiguous downwardly pro- 

 jecting processes in center of the excavation, the apical lateral exten- 

 sions of the stemite dilated apically (Fig. 5); pale gray species, the 

 thorax with three pale brown vittse; anterodorsal surface of hind tibia 

 with ten to twelve setulae from base to apex; halteres yellow. . .hinei sp. n. 

 Fifth abdominal sternite not as above; the species much darker than 

 above and otherwise not as stated IS- 

 IS. Halteres brown or fuscous; very small species, not over three millimeters 

 in length; fifth stemite somewhat similar to that of hinei (Fig. 6); hind 

 tibia with very slender bristles; abdomen with very broad uniform 

 black dorsocentral vitta which covers about one-fourth of the dorsum; 



acrostichals sparse, in two series fuscohalterata sp. n^ 



Halteres yellowish or whitish 14 



14. Arista with the longest hairs at least as long as width of third antennal 



segment; hypopygium as in Figure 21 variata FalleD 



Arista with very short hairs or almost bare 15- 



15. Abdomen short and broad, rather thick, glossy and without distinct 



markings; hypopygium very large sepia Zetterstedt 



Abdomen not as above, always distinctly pruinescent and more or less 

 distinctly marked 16- 



16. Fifth abdominal sternite with dense short bristly hairs, one group which 



is downwardly directed at base of inner margin of each process, and 

 another on apical half of each (Fig. 7); thorax very distinctly vittate; 

 parafacials at least as broad at base of antennse as third antennal 

 segment; hind tibia with three or four anterodorsal bristles; acrostichals 



in two series atrovittaia sp. n. 



Fifth abdominal stemite not bristled as above; species differing in other 

 respects 17 



17. Hind tibia with two series of short setulas on basal two-thirds, one on the 



posterior and the other on the posteroventral surface; small species, 

 three or four millimeters in length; thorax distinctly vittate. 



nidicola Aldrich 

 Hind tibia with at most a few setul^ on posterior surface on basal half. ... 18- 



18. Third and fourth abdominal stemites, each with some very long bristles 



along lateral margins; dorsal abdominal vitta broad. . . .planipalpis Stein 

 Third and fourth abdominal stemites not as above 19 



19. Mid tibia with one or more anteroventral bristles on apical half 20 



Mid tibia without anteroventral bristles 21 



20. Prealar bristle not over one-third as long as the bristle behind it; acro- 



stichals in four series, two of the hairs usually much longer than the 

 others; hypopygium with a short process on disc, near base, on each 



side (Fig. 23) sericea sp. n. 



Prealar over half as long as the bristle behind it; acrostichals in two 

 rather irregular series, setulose, two of them very much longer and 

 stronger than the others; hypopygium without processes on disc 

 (Fig. 17) appendiculata sp. n.. 



21. Eyes separated by distinctly more than width across posterior ocelli; 



orbits very narrow above; interfrontalia with two pairs of fine setulae 

 above middle; prealar half as long as the bristle behind it; hind tibia 

 slightly reddish; veins three and four divergent at apices. . . aliena sp. n. 

 Eyes separated by less than width across posterior ocelli; hind tibia 

 black 22- 



22. Thorax without any strong bristle-like presutural acrostichals, the 



hairs fine, in four series, one pair stronger than the others; hypopygium 



as in Figure 24 incursa sp. n. 



Thorax with at least one pair of bristle-like presutural acrostichals, the 

 hairs all more or less setulose 2S 



23. Mid femur with some long anteroventral bristles 24 



Mid femur without any long anteroventral bristles 25- 



