22 NORTH AMERICAN DIPTERA 



16. Wings lying flat over the back when at rest; metanotum short and 



without a longitudinal groove; femora sometimes swollen. 



(p. 74) CERATOPOGONID^ 

 Wings lying roof-like over the back when at rest; metanotum long and 

 with a median longitudinal groove; legs long and slender. 



(p. 69) CHIRONOMID^ 



17. Wings short and broad, folded roof-like over the body when at rest, 



usually pointed (p. 78) PSYCHODID^ 



Wings long, or if broad, the apex very broadly rounded, always lying 

 flat over the back when at rest IS 



18. Venation very much reduced, several of the veins lacking. 



(p. 101) CECIDOMYID.^ 

 Venation not reduced, the veins strong 19 



19. Basal cells long, extending to or beyond the middle of the wing 20 



Basal cells, especially the second, short, not extending nearly to the 



middle of the wings (p. 67) THAUMALEID^ 



20. Apical veins strongly arched (p. 80) DIXID^ 



Veins straight or nearly so (p. 83) CULICID^ 



21. Fourth posterior cell widely open (p. 59) ANISOPODID^ 



Fourth posterior cell closed (p. 133) RACHICERIDifc] 



22. Empodium developed pulvilliform, the three pads nearly equal 23 



Empodium hair-like or absent 29 



23. Third antennal segment compound, composed of annuli 24 



Third antennal segment simple, usually beai'ing an elongated style or 



arista 27 



24. Squamae large and conspicuous (p. 148) TABANIDiS^ 



Squamae small or vestigial 25 



25. At least the middle tibiae with spurs (p. 146) CCENOMYID^ 



Tibial spurs absent 26 



26. Posterior branch of the third vein ending before the wing-tip. 



(p. 134) STRATIOMYID^ 

 Posterior branch of the third vein ending well behind the wing-tip. 



(p. 155) PANTOPHTHALMID^ 



27. Squamae very large; head very small, placed low down, composed almost 



entirely of the eves, the face and front very narrow or obliterated. 



(p. 203) CYRTIDZE 

 Squamae small; head larger, the face or front broad 28 



28. Middle tibiae with spurs; venation not complex. . . (p. 157) RHAGIONID^ 

 Tibiae without spurs; venation intricate, many veins ending before the 



wing-tip (p- 201) NEMESTRINID^ 



29. Wings rounded apically, with strong veins antei'iorly and very weak, 



oblique ones; coxae not widely separated by the sternum. 



(p. 234) PHORID^ 

 Wings with normal venation or pointed at the apex, or the coxae broadly 

 separated by the sternum 30 



30. Wings pointed at the apex, without crossveins. 



... t f^ (P- 2^2) LONCHOPTERID^ 



