278 E. T. CRESSON, JR. 



10. Abdomen shining, with bases of segments opake ; tibiae and tarsi 



yellow 20. maiiieiisis n. sp. 



Abdomen polished, with only apex of first silvery laterally. 



34. varius n. sp. 



11. Abdomen entirely opake, velvety-brown or black, without trace of 



gray ; halteres brown. 



21. ciugulatus Loew. (velutinus n. var.). 

 Abdomen subopake, more or less cinereous, at most opake-black 



only at bases of segments 13. 



Abdomen shining or polished, with bases of segments more or less 

 velvety-black, at most only first segment and ventral mar- 

 gins cinereous. 



Tibiae largely brownish or black 21. ciugulatus Loew. 



Tibiae yellow, scarcely tinged with brown 22. fuSCUS Loew. 



12. Abdominal fasciae all white. 



Antennae black, short acuminate 6. ? nigricornis Adams. 



Antennae yellow 5. ? flavitarsis Will. 



Antennas black, acute; ultimate section of fourth vein straight. 



Western species 7. alteruatus n. sp. 



Abdominal fasciae faintly grayish, or nearly shining, only first 

 segment white ; ultimate section of fourth vein strongly 



sinuate 8. nigripes Loew. 



Abdomen polished, at most only base cinereous.. 34. varius n. sp. 



13. Antennae yellow. Mexican species 5. ? flavitarsis Will. 



Antennae black 14 . 



14. Abdomen distinctly fasciated with white or gray, but bases of 



segments opake 15 . 



Abdomen not distinctly fasciated, sometimes nearly shining.... 16. 



15. Wings distinctly tinged with brown ; hypopygium subhemispheri- 



cal, small, cleft 9. semifasciatus n. sp. 



Wings hyaline, or gray, only faintly brownish. Missouri species. 



6. ? liigricoriiis Adams. 



16. Hypopygium quadrate in outline, much larger than the short fifth 



segment, with broad apical cleft (Figs. 60-61). 



10. caudatus n. sp. 

 Hypopygium more semicircular, hardly larger than the large fifth 

 segment, with moderate cleft (Fig. 52). 



11. discolor Banks, n. sp. 



17. Antennae short, acute; stigma as long or longer than fourth 



costal section 2. dubius n. sp. 



Antennae abruptly, short acuminate ; stigma shorter than fourth 

 section 1. loewii Kert. 



18. Legs yellow, or, at most with only femora discolored above 19. 



Femora black, at most only extremities yellow 20. 



19. Abdomen subopake ; apices of segments with or without gray 



fascia. 



