September, 1906.] 2Q3 



times very small and loeaJc, close to the tip on the outer side. Of the 

 other legs, the armature of the fore tibiae is limited in all the British 

 species to a single spine, that of the hind tibiae is very variable. 



18 (23) Scutellum loith only two bristles. Ilind tibiae with one spine only, the 



apical spine on middle tibiae verj small or even absent. 



19 (20) Halteres black or blackish ; third joint of anlennx and palpi reddish or 



yellow. 



$ ? . Frons broad, nearly twice as wide as high in male, but 

 less so in female ; wings tinged with yellowish-grey, costa to well 

 beyond the middle of the wing, its first division nearly twice as long 

 as the second in I he male, but only equal to it in the female, fringe 

 very short and dense, second thick vein robust, especially in female ; 

 legs yellow, tinged sometimes with grey and moderately stout, apical 

 spine on middle tibiae usually absent, the spine on hind tibiae below 

 the junction of the upper and middle thii'ds. Taken from spring to 

 autumn. 



1 — 2 mm. — unispinosa, Ztt. 



20 (19) Halteres whitish {nudipalpis) or yellow {autumnal is) ; third joint of 



antennse and palpi black. 



21 (22) Small species (I — 2 mm.) ; male palpi very large^ blunt ended, and with a 



single long terminal bristle, female smaller, and with three or four 

 terminal bristles ; legs moderately stout. 



<J ? . Frons narrow, nearly as high as broad, glossy ; wings 

 clear, costa and all the veins fine and delicate, fi-inge rather long and 

 open, costa short (about to middle of wing), its first division 1^ times 

 the second in both sexes ; legs from rust colour to nearly black, the 

 apical spine on middle tibiae always present. Taken from spring to 

 autumn. 1 — 2 mm. — nudipalpis, Beck. 



22 (21) Large species (3 mm. or more) ; palpi not abnormally large, pointed, and 



with afeio short marginal bristles ; legs very long and slender. 



S . Frons broad, nearly twice as wide as high, dull ; wings 

 greyish, the veins strongly marked, costa long, reaching well beyond 

 the middle, thickened on its outer third, first division 1^ times the 

 second, fringe short and dense ; legs brown, the spine on hind tibiae 

 above the junction of the middle and upper thirds. In the broad 

 frons and wing characters it much resembles unispinosa, with which 

 Becker compares it, while the general slender build and the slim legs 

 recall some of the 3-veined species. 3 mm. — autumnalis. Beck. 



23 (18) Scutellum with four bristles. 



24 (31) Second thick vein furnished with a row of fine bristles or hairs along its 



whole length to the fork ; the apical spine on the middle tibix strong^ 

 that is, as loell developed as the pair in the upper third. 



In all four species under this head the costa is long, reaching well 

 beyond the middle ; joined by the thick veins at wide intervals, so 

 that the first costal division is never longer than the other two 

 together {curvinervis and fennica), and sometimes considerably shorter 



