232 NORTH AMERICAN DIPTERA. 



TABLE OF GENERA. 



1. Fourth longitudinal vein with a widely divergent fork on the front 



side (1, 3) 2 



Fourth longitudinal vein generally without fork; if one is present 

 it is parallel with the main vein. ..... 4 



2. Cilia of the tegulue black, third vein converging to the fourth at 



tip (3), scutellum with four large bristles (b) . Psilopodinus. 

 Cilia of teguhe pale, third vein curving forward at tip (1), scu- 

 tellum with two large and generally two small bristles. . 3 



3. Face wide, vertex deeply excavated (a). . . Psilopus.* 

 Face narrow, vertex scarcely excavated. . Leptorhethum. 



4. Thorax almost as broad as long; head wider than its height or than 



the thorax; face wide, vertex deeply excavated (17, 32). 



Mesorhaga. 

 Head and thorax not as described. ...... 5 



5. Fourth vein bent forward, forming an apical cross- vein; posterior 



cross-vein oblique, parallel with the margin of the wing (6, b) . 



Plagioneurus. 



Posterior cross-vein nearly transverse, usually no apical cross- 

 vein. ...... 6 



6. Hincl metatarsi with large bristles above (35, a, b, d) . 



Dolichopus. 

 Hind metatarsi without large bristles above. ... 7 



7. Hypopygium long, extending forward under the venter (33). 8 

 Hypopygium short, not extending forward under the venter 



(34, one form). 20 



8. Arista plumose (27). ... ... 9 



Arista bare or pubescent. .... n 



9. Face wide, bulging on the lower part (27, 31, 14, a, d) . 



Pelastoneurus. 

 Face narrow. .......... 10 



10. Third antennal joint of male large, elongated, excavated above. 



Leptocorypha. 

 Third antennal joint normal, as in fig. 27. . . Sareionus. 



11. Before the scutellum the posterior third of the dorsum is hollowed 



out, or at least distinctly flattened 12 



Before the scutellum convex as usual. ...... 15 



* +l'o>iosonia of my Catalogue, 1905. 



