3 o2 NORTH AMERICAN DIPTKRA. 



3. Second section of the costa much shorter than the third;* anal cell 



wanting. .......... 4 



Second section of the costa at least as long as the third. . 5 



4. Posterior cross-vein ahsent. ..... Asteia.t 



Posterior cross-vein present (7 and 7 Oscinidae). Sigaloessa.t 



5. Arista hare, except for a single ray near its base; two fronto-orhital 



bristles on each side Cladochseta. 



Arista plumose or with numerous pectinations. ... 6 



6. The costa reaches to the third vein or a little beyond. . . 7 

 The costa reaches to the fourth vein or a little beyond. . . 8 



7. Costa with sparse but conspicuous bristles; thorax arched, bristly 



behind; scutellum with long bristles; abdoman elongate, droop- 

 ing; larger flies (lO, 11) Curtonotum. 



Costa not with bristly pectinations (9). . , Leucophenga.t 



8. Ultimate section of fourth vein seven or eight times longer than the 



penultimate; a single fronto-orbital brittle on each side; no alu- 

 lae; first posterior cell narrowed in the margin. Stenomicra.i? 

 Ultimate section of fourth vein not more than four times the length 

 of the penultimate; first posterior cell not appreciably narrowed 

 in the margin (5,6,8) Drosophila. 



* If first basal cell but little longer than the anal, and the arista bare 

 or pubescent, see Aulacigaster (Agromyzidae) . 



t I do not know Asleia, but the venation of the type species of the 

 genus seems to be almost identical with that of Sigaloissa as figured 

 with the Oscinidae (7), save that the posterior cross-vein is absent. 

 The venation of Si^aloessa as there given is the more typical; that 

 given in fig. 7 herewith is apparently that of Schiner (South America 

 and West Indies). In which family the genera should be placed is at 

 present a mere matter of opinion. 



% Including such species as Drosophila frontalis and perhaps others 

 described as Drosophihc. 



>,, This genus seems to be peculiar in its approximated cross-veins, 

 and single fronto-orbital bristle. I do not know it. 



