KEY TO DIPTERA. 



13. Antennae apparently two-jointed, with a three- 

 jointed arista. Wings (rarely wanting) with strong 

 anterior and much lighter posterior longitudinal veins, 

 usually without discal cell. Small, hunchbacked, quick- 

 running, bristly flies PHORID/E (p. 253) . 



Antennae almost invariably with 3 easily distinguish- 

 able joints, the terminal one being often annulated. Discal 

 cell, as a rule, present 14. 



14. Three nearly equal pulvilliform pads under the tarsal 

 claws. Head and thorax without strong bristles 15. 



Only two pads under the tarsal claws, the median one 

 wanting or represented by a bristly hair. Head and 

 thorax often with bristles 19. 



15. Squamae very large; thorax and abdomen inflated; 

 head small, with relatively large eyes CYRTID.E 



(p. 248). 



Squamae of moderate size or small, or the thorax and 

 abdomen not inflated 16. 



1 6. Third joint of the antennae simple, not composed of 

 superficial rings. Costa enclosing the wing margin 



beyond the tip. Squama? very small, vestigial 



LEPTID^E (p.' 248). 



Third joint of the antennas complex, 4- to 8-ringed, 

 rarely with a distinct bristle-like arista 17. 



17. Costal vein not enclosing the hind margin of the 

 w r ing. Squamas small or vestigial STRATIOMYID.E 



(p. 246). 



Costal vein continuing around the hind margin of the 

 wing 18. 



18. Squamae conspicuous TABANID^E (p. 247). 



Squamae small or vestigial XYLOPHAGID^E. 



19. Third longitudinal vein forked, delimiting two or 

 more submarginal cells 20. 



Third longitudinal vein not forked, but one sub- 

 marginal cell 25. 



20. Anal cell, when present, closed some distance from 

 the hind border of the wing, sometimes absent. Third 

 antennal joint usually with a terminal style. Vertex 

 flat or convex EMPIDID^E (p. 252). 



Anal cell always present, either open or closed in or 

 near the margin of the wing 21. 



233 



