H 4 NORTH AMERICAN DIPTERA. 



9. Fork of the fifth vein petiolate. ...... 10 



Furcation of the fifth vein slightly proximad of the posterior 

 cross-vein. . . . . . . . . . .11 



10. First vein forked at its extremity (9) . . . . Tanypus. 

 First vein simple Trichotanypus Kieffer. 



11. First vein forked at its extremity. Ablabesmyia Johannsen. 

 Fork of the first vein and the second vein pale and indistinct; an- 

 tennae of the female twelve jointed. . leoplastus Skuse. 



12. Fourth tarsal joint shorter than the fifth, obcordate. . . 13 

 Fourth tarsal joint linear. . . . Prodiamesa Kieffer. 



13. Antennae of the male with fourteen plumose joints; terminal joint 



very long; antennae of the female with seven or eight short 

 haired joints (8) Diamesa. 



Antennae of both sexes short-haired, the terminal joint oval; those 

 of the male with nine, of the female with eight joints. 



(The female does not seem to differ from Dianicsa.} 



Eutanypus. 



14. Thorax with a median longitudinal fissure; small species, usually 



with blackish wings having white markings. Chasmatonotus 

 Thorax without longitudinal fissure. . . . . . 15 



15. Claws cleft; first vein ending not far from the tip of wing; anten- 



nae seven jointed in both sexes. . . Telmatogeton. 



Claws not cleft, though sometimes toothed on the side. . 16 



16. First vein thickened at apex, anal angle of wing obsolete; antennas 



of the male with ten or eleven joints, of the female with six 



joints; very minute flies (3) .... Corynoneura. 



Not with all the above characters. . . , . 17 



17. Fourth longitudinal vein simple; antennae of male with foiirteen 



joints, closely sessile, plumose, the terminal joint cylindrical; 

 antennae of the female with seven joints, short haired; (second 

 and third joints sometimes more or less coalescent) . Chirono- 

 mns, sens. lat. ......... 18 



Fourth longitudinal vein furcate; antennae of both sexes fourteen 

 jointed, except with Tersest hes. . . . . . 25 



18. Fourth tarsal joint obcordate, shorter than the fifth; front meta- 



tarsus shorter than its tibia; wing under low magnification bare. 



Thalassomyia. 

 Fourth tarsal joint linear. ....... 19 



