INTEODUCTIOiS^ / 



incomplete. Scutellum often with two or 



four (rarely six or eight) spines on margin. Stratiomyidae, 



6. Antennae flagelliform. Fourth posterior cell [p. 17, 



closed. Wing with marginal space of last 

 submarginal cell at most twice that of 

 immediately adjoining cells. Squamae 

 almost obsolete. Perfect insects never 



blood-suckers Acanthomeridae. 



Antennae normally sickle-shaped, rarely fla- 

 gelliform or otherwise formed. Fourth 

 posterior cell nearly always open. Wing 

 with marginal space of last submarginal 

 cell at least three or four times that of 

 immediately adjoining cells. Squamae 

 very large. Adult females always blood- 

 suckers " Tabanidae. 



7. Posterior tibiae always spurred. Body gene- 



rally elongate, abdomen never balloon-like. 

 Eyes in 3" contiguous, in 2 wide apart ; 

 head of normal size and shape. Thoracic 

 squamae normal. Venation as in Taba- 

 nidae, except that the anal cell is some- 

 times open Leptidae, p. 100. 



All tibias unspurred or with very short blunt 

 ones. Body short, rounded ; abdomen 

 often balloon-like. Eyes in both sexes 

 contiguous ; head very small, inconspi- 

 cuous, depressed, nearly all eyes. Thoracic 

 squamae enormous. Venation eccentric and 

 complex Cyrtidae, p. 157. 



8. Basal cells long, at least one-third the length 



of the wing. Anal cell (sometimes called 

 the third basal) open, or long and pointed. 9. 

 Basal cells short (except in Hybotix.e). 

 Anal cell shorter than preceding cell, when 

 that is present. Third vein never forked, 

 except in some EMPiDiE 18, 



9. Posterior cells parallel vv^ith hind margin of 



wing. Second longitudijial vein (and some- 

 times upper brancli of third also) ending 

 in first longitudinal near its tip. Antennte 

 generally clavate at tip. Eyes in J dis- 

 tinctly separated Mydaidae, p. 314. 



Posterior cells not parallel with hind njargin 

 of wing. Second longitudinal vein ending 

 in first only in Apiocerio^^ and some 

 AsiLiD^ ; in all other families ending in 

 wing-margin. Antennae not clavate at 

 tip. Eyes in c? contiguous or well sepa- 

 rated 10. 



10. Upper branch of 4tli A^ein ending before 



wing-tip 11. 



Upper branch of 4th vein ending below 

 wing-tip 12 



11. Venation more complex. Five posterior cells, 



the 4th closed. Eyes in cJ always wide 



