2 PROCEEDINGS OF THE NATIONAL. MUSEUM. vol.60. 



Male antennae with the second joint rudimentary and the arista elongated and 

 ending in a lamella ; fourth vein ending considerably before the apex, very 

 close to the tip of the third vein Maeellocerus. 



The common or general characters of Tachytrechus are as follows : 

 First antennal joint hairy above, arista dorsal, face long, narrow, 

 wider below and with the tip rounded, reaching as low as the inferior 

 border of the eye; wings narrow, in the male especially, but rather 

 broad in one species [T. rotundipennis] ; hypopygium of the male 

 entirely disengaged, directed forward under the venter, reaching 

 nearly to the coxae ; hind metatarsi without bristles above. 



The characters used by Mik to separate Maeellocerus from Tachy- 

 trechus were mostly male characters. After a careful study of the 

 two genera I consider them to be one genus, although the males do 

 divide satisfactorily into two groups by the antennae. 



The genus divides naturally into three groups on the male char- 

 acters: 1, wing with a maculation at the apex; 2, arista very long 

 with a lamella at the tip; wing without maculation; 3, arista short 

 and normal; wing without maculation. 



Genus TACHYTRECHUS Haliday. 



Key to the males. 



1. Wing with a black spot at the apex 2. 



Wing without a spot 6. 



2. Spot large, round with a very narrow hyaline border around the lower edge; 



no snow-white spot No. 4. fioridensis Aldrich 



Spot blacli with a snow-white spot behind it '6. 



3. White spot nearly equal in size to the black spot 4. 



White spot much smaller than the black spot 5. 



4. White spot at apex of wing, rounded and nearly equal in size to the black 



one; wing narrow and pointed No, 3. vorax I^ew. 



White spot like a half crescent ; black spot very large and rounded ; wing 

 very broad and rounded No. 2. rotundipennis, new species. 



5. Black spot long, narrow and pointed below; white spot very long and 



narrow No. 1. simulatus, new species. 



Black spot large; white spot very small and hemispherical. 



No. 5. volitans Meluniier. 



6. Arista short, normal, no lamella 7. 



Arista very long, with a terminal lamella *__9. 



7. Hind tibiae with two or three flattened bristles on the posterior side. 



No. 15. angustipennis Loew. 

 Hind tibiae without such bristles 8. 



8. Middle tarsus with the second joint extremely broad, flattened, tarsus con- 



spicuously ornamented No. 14. g^anditarsus, new species. 



Middle tarsus normal, except the third joint is slightly bent. 



No. 16. protervus Melander. 



9. Arista with a lamella at the apex and another in the middle. 



No. 6. binodatus Loew^ 

 Arista with a lamella at the apex only IC 



