361 



— Thorax with at least bhick diseal marks ; wings marked otherwise 



than as above 4 



4. Thorax and seutellum black 5 



— Ground color of thorax yellow, disc with black marks, seutellum 



yellow 6 



5. Setulose hairs on f rons and cheeks black ; wings with very distinct 



infuscation, which extends to base and is most distinct in cell 



bounded by first vein and costa ; legs entirely yellow (111.) 



pallidipes, n. sp. 



— Setulose hairs on f rons and cheeks yellow ; wings with rather indis- 



tinct infuscation, which does not extend to base ; legs yellow, hind 

 femora and tibiae largely black (111.) fumipennis Malloch. 



6. Sides of mesonotum near anterior angles with a white spot (111.) . . . 



splendidus Malloch. 



— Sides of mesonotum without a white spot (Mass.) 



ohscuripennis Johnson. 



7. Thorax and seutellum glossy black ; apical half of hind femora black, 



the remainder of legs yellow (La.) pilosidns Becker. 



— Either disc of mesonotum or the seutellum yellow; legs not as above 



8 



8. Halteres yellow 9 



— • Halteres black 11 



9. Seutellum black, disc of mesonotum yellow, with a posteriorly tri- 



dentate black mark which covers almost the entire disc (Pa., 111., 

 N. H.) dorsalis Loew. 



— Seutellum yellow, with brownish marks upon the disc 10 



10. Disc of mesonotum with 3 confluent black vittae, forming a large dis- 



eal mark, rarely nan'owly separated ; seutellum with a ])asal l)lack 

 mark on each side (N. H.) epliit^pmm. Zetterstedt. 



— Disc of mesonotum with 3 black spots, the rudiments of the normal 



vittae, beyond middle; seutellum with a large brownish mark on 

 disc (111.) interrupins, n. sp. 



11. Legs entirely yellow or with only a faint brownish mark at apices of 



hind femora (N. H., Vt., 111.) montanus Coquillett. 



— Legs with distinct, deep black marks 12 



12. Thorax glossy black, lower half of pleurae and the seutellum yellow 



(111.) apicalis Malloch. 



Thorax and seutellum yellow, disc of the former with black marks 

 (Pa.) festivus Loew. 



Gaurax fi,avidui.us, n. sp. 



Male. — Yellow, subopaque. Head yellow, ocellar region, inner 

 upper mouth-margin, and back of head black. Thorax yellow, a black 

 central spot on pleurae and a similarly colored transverse one on mid- 

 dle of postnotum. Abdomen yellow, infuscated on sides of first seg- 



