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; scutellum with 



six bristles Plethochaeta Coquillett. . . . 



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



4. Arista plumose Pycnoglossa Coquillett. . . 



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 



Trichopol pus Rondani, pt. 

 (Chaetosia Coquillett) 



7. Pteropleura bare 8 



Pteropleura hairy on at least part of its surface 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 Coquillett. 

 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 1 Hydromyza Fallen . 



Orbital bristles long; discal cell closed at base 10 



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



Acanthocnema Becker. 



Fore tibiae without such rectangularly projecting spine 10a 



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



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 cell 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 if so the arista is bare or almost so. . 13 



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



legs stout , Cordylura Fallen, pt . . 



Presutural dorso-central bristle's weak or absent, prothoracic and stigmatal bristles weak; 

 humeral usually absent; tibia? usually with very weak bristles. Paralleloma Becker, pt. 



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



Bucephalina, n. gen. 

 Scutellum 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 genitalia without such bristles; fore tibia? 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 wing-vein extending to margin 18 



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



Paralleloma Becker, pt. 

 Arista almost bare; eyes rounded; legs short Cordylurella, 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 half 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. 



