76 c Canadian Arctic Expedition, 1913-18 



Key to Genera — Con. 



3. Palpi with long apical bristle which is about as long as the palpus; scuteUum with 



six bristles Plethochaeta CoquiUett. . . . 



- Palpi without long apical bristle; scutellum with two or four bristles 4 



4. Arista plumose Pycnoglossa CoquiUett . . . 



Arista alomost bare , .' 4a 



4a. Fore femora with anterior and antero-ventral surfaces armed with closely placed 



black bristles Amaurosoma Becker .... 



Fore femora without such bristles Pselaphephila Becker. 



5. Third antennal joint with apex rounded; scutellum with two bristles Hexamitocera Becker. 

 Third antennal joint with upper portion of apex acute or angulate; scutellum with 



four bristles. 6 



6. Arista much thickened on basal half, the second joint much longer than thick, genicu- 



lated with third Gonatherus Rondani. 



Arista thickened at base, second joint about as long as thick, not geniculated apicaUy 



Trichopalpus Rondani, pt. 

 {Chaetosia CoquiUett) 



7. Pteropleura bare , 8 



Pteropleura hairy on at least part of its sm-face 22 



8. Head much longer than high, face much retreating below; palpi with long apical 



bristle, third antennal joint with a long hair on outer side near base of arista. . . . 



Acicephala CoquiUett. 

 Head at least as high as long, face not much retreating below; third antennal joint 

 without long hair as above 9 



9. Orbital bristles very short, distinguishable only with strong lens; cross-vein absent 



from base of discal cell' Hydromyza Fallen. 



Orbital bristles long; discal ceU closed at base 10 



10. Fore tibiae with a short, stout, rectangular spine near apex on under side 



Acanthocnema Becker. 



Fore tibise without such rectangularly projecting spine j . 10a 



10a. Fore femur and fore tibiae each with a series of strong bristles on antero- and pbstero- 



ventral surfaces Norellia Robineau-Desvoidy. 



Fore femur without strong bristles on antero-ventral surface; bristles on tibia not in 



two series 10b 



10b. Third and fourth wing-veins curved downward on their penultimate sections, the first 

 posterior ceU proximad of inner cross-vein distinctly broader than at any other 

 point; stigmatal bristle absent; arista pubescent; palpi with long apical bristle;, 



first vein bristly at apex Scoliaphleps Becker. 



Wing venation normal, first posterior cell proximad of inner cross-vein not broader 



than at any other point 10c 



10c. First wing-vein bristly on apical half 11 



First wing-vein bare on apical half 16 



11. Palpi long and slender, armed at apices with a long bristle; arista plumose 12 



Palpi not armed at apex with a long bristle, or it so the arista is bare or almost so. . 13 



12. Presutrual dorso-central, prothoracic, stigmatal, humeral, and tibial bristles strong; 



legs stout f Cordylura FaUen, pt . . 



Presutural dorso-central bristlefs weak or absent, prothoracic and stigmatal bristles weak; 

 humeral usuaUy absent; tibiae usuaUy with very weak bristles. ParaZZeZoma Becker, pt. 



13. ScuteUum with six bristles; lower margins of cheeks with numerous long bristles. . . . 



Bucephalina, n. gen. 

 ScuteUmn with two or four bristles 14 



14. Male genitalia with very long curled bristles on each side which are directed upward 



and slightly forward; fore tibiae with short, black spines on inner side 



Pogonota Zetterstedt. 

 Male genitaUa without such bristles; fore tibiae without short black spines on inner side 15 



15. Arista subnude; intra-alar bristles absent Gimnomera Rondani. 



Arista plumose, the hairs widely separated; intra-alar bristles distinct 



Megophthalma Becker. 



16. Sixth wing-vein not extending to margin 17 



Sixth witig-vein extending to margin 18 



17. Arista plumose; eyes concave on lower posterior margin; legs long and slender 



PoraZZeZoma Becker, pt. 

 Arista almost bare; eyes rounded; legs short Cordylwella, n. gen. 



18. Prealar bristle more than half as long as the bristle behind it; thoracic and leg bristles 



long and atrong 19 



Prealar bristle much less than haU as long as the one behond it; thoracic and leg 

 bristles of moderate length ; 20a 



*This last character does not apply to the European species. 



