224 NORTH AMERICAN DIPTRRA. 



5. Third longitudinal vein simple. ...... 6 



Third longitudinal vein branched. ...... 7 



6. Anal cross-vein parallel with the hind margin of the wing (13). 



Oreothalia. 



Anal cross-vein perpendicular to the hind margin of the wing (6). 



Heleodromia. 



7. Head longer than broad, extending forward; wings brown with 



numerous pale spots. .... Dolichocephala. 

 Head transverse, nearly vertical. .... Clinocera. 



BRACHYSTOMATIN^. 



Anterior branch of third vein terminates in the second vein (14) . 



Blepharoprocta. 

 The anterior branch of the third vein terminates in the costa. 



Brachystoma. 



HYBOTIN^S. 



1. Fourth vein forked; hind femora slender. .... 2 

 The discal cell emits two simple posterior veins; hind femora more 



or less thickened; antennae with a slender arista. . . 3 



2. Third longitudinal vein furcate; no antennal style (5, 1O) Prorates. 

 Third vein simple; antennae with a thickened style. Megiiyperus. 



3. The second vein arises near the base of the wing (25) . Syneches. 

 The second vein arises near the middle of ihe wing. . . 4 



4. Vein between basal cells indistinct. . Syndyas. 

 Veins between basal cells strong (1, 21). . . . Hybos. 



OCYDROMIIN^;. 



1. Discal cell present. ......... 2 



Discal cell wanting. ......... 9 



2. The discal cell emits three simple posterior veins. ... 3 

 First posterior vein obsolete; antennae with a long, slender arista. 8 



3. Third antennal joint short, ovate, pointed, with a long arista; third 



longitudinal vein simple. .... Parathalassius. 

 Antennas with a short, thick style. ...... 4 



4. Third longitudinal vein furcate; last antennal joint short and broad. 



Hormopeza. 

 Third vein simple. . ..... 5 



5. Hind femora spinose below, thickened; hind tibiae shortened, bow- 



ed near the knee; last antennal joint large. . Oedalea. 



