423 



6. Wings vitreous, veins almost colorless ; third and fourth veins dis- 



tinctly divergent towards apices, the former ending appreciably 

 farther in front of apex of wing than fourth does behind it (PI. 

 XXXIX Fig. 15) 46. griseus. 



— Wings slightly grayish, veins yellowish brown ; third vein bent 



downward as it nears apex of wing, ending at about the same dis- 

 tance from apex of wing as fourth does 47. maiurus. 



7. Large species, averaging more than 4 mm. in length ; abdominal seg- 



ments with pale posterior margins 9 



— Small species, averaging 2.5 mm. in length 8 



8. Abdomen entirely black, fore tibiae yellow 44. lialteralis. 



— Abdomen yellowish on basal 2 segments ; fore tibiae blackened 



45. nitidellus. 



9. Thorax glossy black ; halteres black apically 43. fuscicornis. 



— Thorax subopaque, distinctly gray pruinescent; halteres yellow. . . 



47. maturus. 



10. Mesonotum with reddish vittae, a conspicuous black or brown mark 



on center of anterior half of median vitta 11 



— Mesonotum with the median vitta unicolorous, black or reddish . . 12 



11. Bright green species ; the black mark on median vitta linear ; lateral 



vittffi unicolorous reddish 48. festivus. 



— Eeddish yellow species ; the dark mark on median vitta in the form 



of a wedge, its apex directed caudad ; lateral vittse brown on 



outer margins, shading gradually into red on inner margins 



49. dorneri. 



12. Males 13 



— Females 28 



13. Apices of abdominal segments narrowly black or brown 14 



— Apices of abdominal segments not narrowly darkened 15 



14. Large species, averaging 8 mm. in length ; fore tarsi with very long 



hairs on posterior surface from middle of first to apex of fourth 

 joint ; hypopygium as in Figure 14, Plate XXXIII . . .48. festivus. 



— Small species, not more than 3.5 mm. in length ; hairs on fore tarsi 



rather short, those on third joint longest; hypopygium as in Fig- 

 ure 1, Plate XXXIV 50. illinoensis. 



15. Abdominal segments each with a brown fascia at middle, rarely 



reaching to base of segments ; plumes of antenme bicolored, form- 

 ing a broad brown ring at bases and another, narrower one, be- 

 yond middle, the rings separated by a narrow whitish band, apical 

 portion whitish; hypopygium as in Figure 11, Plate XXXIII. . . . 

 51. decorus. 



— Abdomen without median fasciae on segments; plumes of antennae 



rarely forming colored annuli 16 



16. Second joint of fore tarsi longer than fore tibiae 17 



— Second joint of fore tarsi shorter than fore tibiae 18 



