ORTAUDIM). 275 



1. The picture of the wings consists chiefly of a dark border along the 



costa, from the base of the stigma to the tip of the wing, with 

 the first basal cell and the posterior cross-vein clouded; anterior 

 cross-vein oblique. ........ 6 



Flies not having the above characters. ..... 2 



2. Posterior angle of the anal cell drawn out into a sharp point. 



Ostracocoelia. 

 Posterior angle of the anal cell rounded. ..... 3 



3. Picture of the wings dark, varied with transparent spots and bars. 4 

 Wings not so marked. ........ 5 



4. Scutellum large, flat; occiput but little swollen ; veins of wings 



straight and markedly divergent. . . Amphicnephes. 



Scutellum smaller, not flattened; occiput much smaller; epistoma 



strongly projecting; third and fourth longitudinal veins nearly 



parallel, sinuous Platystoma. 



5. The picture of the wings consists of four blackish cross-bands, of 



which the third is nearly perpendicular, and the fourth lies 

 along the costa at the apex of the wing; scutellum with four 



bristles (5) Rivellia. 



Wings without bands; scutellum with two bristles; ant-like flies. 



My rmecomyia . 



6. Posterior cross-vein prolonged beyond the fourth vein; scutellum 



with six bristles, . . . . . . Himeroessa. 



Posterior cross-vein not prolonged 7 



7. Fifth longitudinal vein bristly. .... Briciniella. 

 Fifth longititdinal vein not bristly;* scutellum with four bristles (2) . 



Stenopterina. 

 CEPHALIIN^;. 

 Oral opening very large; clypeus and proboscis greatly developed; 

 propleural bristle absent; mesopleural bristle present; sixth segment 

 of the abdomen in the female distinctly developed; ovipositor flatten- 

 ed; first longitudinal vein bristly. 



1. Slender, Sepsis-like flies, resembling Myrmecomyia, with wings 

 almost hyaline, except for a small infuscation at the stigma and 



at the tip • . . . Cephalia. 



Wings with a conspicuous picture. ...... 2 



* I can not see wherein Bricinnia Walker, to which Giglio-Tos re- 

 fers a Mexican species, differs from Stenopterina. 



