NORTH AMERICAN DIPTERA. 171 



fi. — Pile of ahdomeii largely black ; base of third anteniial joint sbort-couical..". 

 Pile of abdomen white; body destitute of black pile ; base of third anteniial 



joint elongate-conical; claws of front tarsi minute 55. ciin'facta. 



7. — Claws of front tarsi minute, scarcely one-fourth as long as those of the 



other tarsi; breast destitute of black pile 8. 



Claws of front tarsi larger, about one-half as long as those of the other 

 tarsi ; l)reast provided with black pile ; tomentum of occiput pure white. 



14. anna. 



8. — Tomentum of occiput pure white, a white tomentose cross-band on front 



part of thorax- passing above the wings and crossing base of scutcUuni. 



56. in<Milta. 

 Tomentum of occiput light yellow; no white tomentose cross-band on tho- 

 rax and scutelluni 57. f«'rr»'na. 



9. — Sides of abdomen destitute of long scales 10. 



Sides of abdomen with a fringe of long scales ; face greatly retreating below ; 

 tomentum of the third abdominal segiuent wholly black. 



58. squaiui;i;era. 

 10. — Abdomen having black pile on sides of some of the segments anterior to 



the fifth 11. 



Abdomen destitute of black pile on sides of any segment anterior to the 



fifth 22. 



11. — Third antennal joint short-conical or subglobular at its base, then suddenly 



constricted, the terminal portion styliform 12. 



Third antennal joint gradually tapering from base to apex, destitute of a 

 long styliform portion ; tomentum of body largely brassy-yellow ; front 



tibiie destitute of bristles 59. geniolla. 



12. — Front tibise provided with bristles 13. 



Front tibia- destitute of bristles 16. 



13. — Tomentum of abdomen never bronze-colored, or if approaching this color 

 then the third segment is furnished with light colored tomentum... 14. 

 Tomentum of abdomen largely, of thorax and scutelluni wholly bronze- 

 colored ; third segment of abdomen destitute of light-colored tomentum ; 



legs black 4. a'nea. 



14. — Black and light-colored tomentum of abdomen not forming distinct cross- 

 bands 15. 



Black and light-colored tomentum of abdomen forming distinct alternating 

 crosis-bands ; pile on sides of fourth segment largely or wholly whitish ; 

 tomentum of occiput yellowish; base of wing of male furnished with 

 an epaulette of silvery scales ; last segment in the male destitute of 



silvery tomentum 7. alleriiata. 



15.— Tomentum of thorax yellowish ; pile of pleura and of breast white, length 



of body less than nine mm 15. snpiiia. 



Tomentum of thorax black; pile of pleura and of breast largely black; 

 that on third abdomiiuil segment largely or wholly black ; length of 



body over 12 mm 7a. liypoinolas. 



16. — Abdomen destitute of bronze-colored tomentum 17. 



Abdomen largely bronze-colored tomentose; last segment in tiie male fur- 

 nished with silvery tomentum ; no epaulette of silvery scales at base 

 of wings 5. nebnlo. 



TRANS. AM. ENT. SOC. XIX. JUNE, 1892. 



