240 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.46. 



3. Mesonotum with diecal hairs arranged in regular longitudinal rows of three to 



five 4 



Mesonotum with discal hairs indiscriminately arranged, or in more than five rows. 

 (These rows are considered as including the two lateral, generally punctate, 

 rows and that space between them, but not the space beyond these rows lat- 

 erally.) 5 



4. The space between the center and lateral rows of discal hairs bare except for 3-4 weak 



hairs on anterior half of mesonotum; frontal triangle barely extending mid- 

 way to anterior margin of frons, almost entirely bare; arista bare; scutellum with 



apical bristles yellow, approximated 2. nudifrons, new species. 



The space between the central and lateral rows of hairs on disk occupied on its 

 entii-e length by a regular series of short, hairs; fi'ontal triangle extending to 

 almost the anterior margin of frons, its sides convex; third antennal joint black- 

 ened on dorsal surface; arista with short pubescence; apical bristles on scutel- 

 lum not closely approximated 3. nitidifrons, new species. 



5. Frontal triangle brownish yellow, only black on center, sides concave; head 



otherwise yellow; hind tibial spur about as long as diameter of tibia. 



4. peruanus Becker. 



Frontal triangle black, its sides straight; head not otherwise entirely yellow; 



hind tibial spur distinctly longer than diameter of tibia 6 



6. Cheeks, except anterior margin narrowly, black; base of abdomen yellow; mid 



and hind coxae generally darkened 5. Jlavipes Loew. 



Cheeks, except posterior margin narrowly, yellow; abdomen with three longi- 

 tudinal rows of black spots; mid and hind coxae yellow. 



Jlavipes, var. hicolor Coquillett. 



7. Mesonotum glossy black; legs mostly pale yellow, the tibiae for the greater part 



of that color, with generally only a more or less distinct brown, or black, band 



on hind pair 8 



Mesonotum, if glossy black, obscured by brown or whitish dusting; or legs mostly 

 brownish or black; or mesonotum brownish, or yellow, with or without dusting 

 or markings 11 



8. Scutellum yellow, black at base 6. scutellnris Williston. 



Scutellum concolorous with mesonotum 9 



9. Antennae yellow; arista distinctly longer than breadth of frons; frons almost 



entirely black; scutellum truncate behind, the apical bristles situated widely 



apart on short tubercules 7. truncata, new species. 



Thh'd antennal joint generally distinctly darkened above; arista shorter than 

 breadth of frons; scutellum rounded behind 10 



10. Hind femora and hind tibiae blackened (in apical half. . 8. apicata, new species. 

 All femora more or less blackened or browned on middle. 



Jlavipes, var. pusio Loew. 



11. Mesonotum entirely black, with more or less distinct grayish dusting 12 



Mesonotum yellow, or reddish, with or without dusting or markings 21 



12. Legs mostly black ; mesonotum slightly dusted 13 



Legs almost entirely yellow; mesonotum thickly dusted 18 



13. Frons with lateral hairs in form of bristles 13a 



Frons with only hairs on lateral margins 14 



13a. Triangle dusted, opaque capax ' Coquillett. 



Triangle highly polished gracilis, new species. 



14. Third antennal joint yellow or reddish below 15 



Third antennal joint entirely black 16 



1 This species and gracilis I have put in a separate genus—Pseudohippelates—h\it included them here 

 for convenience. 



