INSE;CUT0R INSClTL^i menstruus 133 



18. Northern species (tristis complex) tristis Lw. 



Southwestern species (see ?) sororocula Will. 



19. Arista noticeably longer than width of frons measured at 



antennae ; scutellum with a transverse, shallow groove run- 

 ning parallel with posterior margin 20 



Arista much shorter than width of frons measured at base of 

 antennae 21 



20. Pile on frons and mesonotum luteous ; styles very long and 



slender ; costa, from base to tip of auxiliary vein, with con- 

 spicuous long black hairs (Virginia, District of Columbia, 



Maryland, Pennsylvania) capillata Loew. 



Pile on frons and anterior corners of mesonotum black ; in- 

 conspicuous hairs on costa except at base, styles short and 

 broad slossonce, n. sp. 



21. Frons nearly bare (Nebraska) laevifrons Jones. 



Frons well clothed with long pile 22 



22. Only a slight trace of silvery pruinosity on frons, the pile 



dark (Colorado) tarda Snow. 



Pile on frons light, the silvery pruinosity very apparent when 



specimen is held in proper reflection 23 



23. Pile on anterior part of mesonotum as long as pile on frons 



(Colorado) brevichaeta, n. sp. 



Pile on mesonotum half as long as on frons 24 



24. Head greatly enlarged (Indiana) caltha, n. sp. 



Head moderately enlarged (Canada) comosa Lw. 



Cartosyrphus — Females 

 Eyes bare 



1. Arista with very long loose, or very dense plumosity ; scutel- 



lum with bristles Hiatomyia 2 



Arista short plumose, pubescent or bare Cartosyrphus 12 



2. Arista thickly plumose ; pile on mesonotum largely luteous 



(signatiseta group) 3 



Arista with scattered long rays; pile on mesonotum largely black. . .5 



3. Third antennal joint unusually large, about fifteen times that 



of the second, and bright yellow in color ; arista very 



densely plumose (Idaho) signatiseta Hunter 



Third joint only half tliis size, or less; arista less thickly plumose.. 4 



4. Mesopleurae with only light pile; mesonotum with a near 



golden colored pile, the scutellar bristle hairs concolorous 



(British Columbia) canadensis, n. sp. 



Mesopleurae with tuft of long, coarse black hairs ; pile of 

 mesonotum duller in color ; black bristle-like hairs on scutel- 

 lum (Colorado) gcviiui, n. sp. 



