The True Flies 



Face perpendicular and somewhat projecting forward on its 

 lower part, palpi minute, third and fourth veins parallel 

 or diverging toward their apices Family Sepsidce. 



52 — Femora and usually the body short and robust 54 



Femora slender and elongated, body also usually elongated, 

 anal cell present 53 



53 — Fourth vein parallel with or diverging from the third vein . . 

 Family Psilidce. 



Fourth vein usually curving toward the third at its apex 

 (Micropeiidce, in couplet 51). 



54 — Head nearly hemispherical, not prolonged laterally 55 



Head prolonged laterally, the eyes situated at the apices of 



the prolongations, front femora very robust 



Family Diopsidce. 



55 — Anterior oral margin bearing a distinct bristle on either 

 side 58 



Anterior oral margin not bearing such bristles 56 



56 — Anal cell usually wanting, the second basal cell usually con- 

 fluent with the discal cell 57 



Anal cell distinct, second basal cell usually separated from the 

 discal cell ( Agromy^idce, in couplet 60). 



57 — Antennal arista frequently long-pectinate on the upper side, 

 head usually much wider than high, face usually pro- 

 vided with bristles especially on each side, and the oral 



opening sometimes excessively large 



Family Ephydridce. 



Antennal arista never long-pectinate, head not wider than 

 high, face not bristly, and the oral opening never un- 

 usually large Family Oscinidce. 



58 — Arista of antennas bare, body short and robust 60 



Arista usually plumose; if bare the [body is some what 

 slender 59 



59 — Hairs of the antennal arista long and few in number, second 



basal cell usually confluent with the discal cell 



Family Drosophilidce. 



Hairs of the arista short and numerous, sometimes wanting; 



second basal cell separated from the discal cell 



Family Geomy^idce. 



92 



