32 NORTH AMERICAN DIPTERA. 



8. Posterior cross-vein situated before the middle of the wing; three pos- 

 terior cells present (West Indies). . . THAMBETA Williston. 

 Posterior cross-vein not situated before the middle of the wing. . 4 



4. A single submarginal cell present. 5 



Two submarginal cells present. .... . . . 7 



5. Antennae 14-jointed. . ,. ! . . . . LIMNOBIINI. 

 Antennae 16-jointed. . ,.- . ...- . . ' :. . . 6 



6. Tibiae with spurs at the tip ; the first longitudinal vein usually ends in 



the second. . CYLINDROTOMINI. 



Tibiae without spurs ; the first vein ends in the costa. . ANTOCHINI. 



7. Tibiae without spurs at the tip. . . . . . ERIOPTERINI. 



Tibiae with spurs at the tip 8 



8. The subcostal cross- vein is beyond the origin of the second longitudi- 



nal vein 9 



The subcostal cross-vein is before the origin of the second longitudinal 

 vein AMALOPINI. 



9. Antennae composed of sixteen joints. . . . LIMNOPHILINI. 

 Antennae composed of from six to ten joints, often much elongated. 



ANISOMERINI. 



LIMNOBIINI. 



1. Proboscis longer than the head and thorax together. 



GERANOMYIA Haliday. 

 Proboscis shorter than the head and thorax together. ... 2 



2. Antennae pectinate or subpectinate, at least, in the male. 



RHIPIDIA Meigen. 

 Antennae not pectinate. ......... 3 



3. A supernumerary cross-vein between the sixth and seventh veins. 



THROCHOBOLA Osten Sacken. 

 No cross- vein connecting the sixth and seventh veins. ... 4 



4. Tip of the auxiliary vein usually opposite, or before, or only a short 



distance beyond the origin of the second vein ; marginal cross- 

 vein always at the tip of the first longitudinal vein ; legs slender. 



DICKANOMYIA Stephens. 



Tip of the auxiliary vein usually far beyond the origin of the second 

 vein ; marginal cross- vein sometimes at the tip but often some dis- 

 tance before the tip of the first vein; legs comparatively stout. 



LIMNOBIA Meigen. 



