INTRODUCTION. 



incomplete. Scutellum often -with two or 



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



6. Antennae flagelliform. Fourth posterior cell [p. 1^ 



closed. Wing with marginal space of last 

 suhmarginal cell at most twice that of 

 immediately adjoining cells. Squamse 

 almost obsolete. Perfect insects never 



blood-suckers Acanthomeridae. 



Antennse 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. Squamse 

 very large. Adult females always blood- 

 suckers Tabanidae. 



7. Posterior tibia? always spurred. Body gene- 



rally elongate, abdomen never balloon-like. 

 Eyes in rf contiguous, in $ wide apart ; 

 head of normal size and shape. Thoracic 

 squamse normal. Venation as in Taba- 

 nidje, except that the anal cell is some- 

 times open Leptidae, p. 100. 



All tibiae 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 

 squamse 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 Hybotixje). 

 Anal cell shorter than preceding cell, when 

 that is present. Third vein never forked, 

 except in some E:\iPiDiE 18. 



9. Posterior cells parallel with hind margin of 



wing. Second longitudinal vein (and some- 

 times upper branch of third also) ending 

 in first longitudinal near its tip. Antennse 

 generally clavate at tip. Eyes in <5 dis- 

 tinctly separated Mydaidae, p. 314. 



Posterior cells not parallel with hind margin 

 of wing. Second longitudinal vein ending 

 in first only in ApiocEBioiE and some 

 Asilid^; ; in all other families ending in 

 wing-margin. Antennae not clavate at 

 tip. Eyes in $ contiguoiis or well sepa- 

 rated 10. 



10. Upper branch of 4th vein 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 J always wide 



