( 3 g NORTH AMERICAN DIPTERA. 



9. Upper branch of the fork of the fourth vein incomplete at the 



base; third vein sinuous (Odonlofioda) . . . Anaclinia. 



Fork of fourth vein complete; third vein not markedly sinuous. 10 



10. Furcation of the fifth vein before or opposite the furcation of the 



fourth. .......... 1 1 



Furcation of the fifth vein distinctly more distal than that of the 

 fourth (12) Phthinia. 



11. The costal vein continues beyond the tip of the third vein; abdo- 



men cylindrical Boletina. 



The costal vein terminates at the tip of the third vein; abdomen 

 compressed Leptomorphus 



12. Auxiliary vein elongated, terminating angularly in the first vein, 



near the origin of the third Syntemra. 



Auxiliary vein vestigial or ending acutely in the first vein before 

 the origin of the third. ....... 13 



13. Fifth longitudinal vein not furcate . . . Zygomyia. 

 Fifth longitudinal vein furcate. ...... 14 



14. The costal vein extends a little beyond the termination of the 



third vein. .......... 15 



The costal vein terminates at the tip of the third vein. . 17 



15. Forked cell of the fifth vein acute proximally, the branches grad- 



ually and but little divergent Epicypta. 



Forked cell of fifth vein less acute proximally, the branches more 

 widely and rapidly divergent, the upper branch curved. 16 



16. Auxiliary vein of considerable length, terminating in the first vein. 



Docosia. 

 Auxiliary vein short, ending free a little beyond the humeral cross- 

 vein Phronia. 



17. Auxiliary vein reaching beyond middle of first basal cell, and ter- 



minating in first vein. ..... Trichonta. 



Auxiliary vein vestigial, or not reaching as far as the middle of the 

 first basal cell. ......... 18 



iS. Furcation of the fourth vein before the first section of the third 



vein 19 



Furcation of fourth vein beyond the first section of the third 

 vein. ........... 20 



