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 Avith 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 iipper portion of apex acute or angulate; scutellum with 
foiu: bristles 6 
6. Arista much thickened on basal half, the second joint much longer than thick, genicu- 
lated with thu'd Gonatherus Rondani. 
Arista thickened at base, second joint about as long as thick, not geniculated apically 
Trichopalpits 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^ .Hydromyza Fallen. 
Orbital bristles long; discal cell closed at base 10 
10. Fore tibiae 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 bristles weak or absent, prothoracic and stigmatal bristles weak; 
humeral usually absent; tibiae usually with very weak bristles. Pa ra/icZo/Ha 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 cm-led 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 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 
Megophthahna 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. 
