166 BR. J. ENT. NAT. HIST., 6: 1993 



10 Apical spot large and extending well behind vein M; wings narrow, their width 

 17-23% of their length (Fig. lb). First postsutural dorsocentral seta about half or 

 less the length of the presutural dorsocentral seta G. apicalis (Meigen) 



— Apical spot of the wing not extending behind vein M, or if so then only faintly; 

 wings broader, their width very rarely less than 23% of their length measured to 

 the root (Figs le-g). First postsutural dorsocentral seta not much smaller than the 

 presutural dorsocentral seta 11 



11 Surstylar lobes shallowly bifurcated at the tips (Fig. 4b). Thorax yellow, often 

 with a distinct reddish tinge along the notopleura and top of each anepisternum, 

 and usually with dark brown marks outside of the postsutural dorsocentral 

 setae; postnotum dark. Crossvein r-m pale though may be surrounded by a faint 

 cloud; length of the apical wing spot short, usually less than twice the length of 

 the r-m crossvein; wings broader, their width about 28-33% of their length 

 (Fig. lg) G. venusta (Meigen) 



— Surstylar lobes of males with simple-ended tips. Thorax more or less uniformly 

 yellow; postnotum pale or dark. Crossvein r-m dark and surrounded by a small 

 dark cloud; length of the apical wing spot obviously twice or more the length 

 of the r-m crossvein; wings narrower, their width usually about 23-28% of their 

 length 12 



12 Tips of the surstylar lobes terminate in an inwardly directed finger-like extension 

 (it is essential to get a clear view of the tip) (Fig. 3c). Postnotum yellow, or at 

 least more similar in colour to the rest of the thorax than to the abdomen. Females 

 are not separable G. balachowskyi Mesnil 



— Tips of the surstylar lobes curved backwards with a slightly expanded rectangular 

 end (Fig. 3e). Postnotum obviously darker than the rest of the thorax in all male 

 specimens seen G. hackmani Nartshuk 



13 Thorax dark brown. No subvibrissal seta is markedly stronger than any other 

 (Fig. 4i) 14 



— Thorax orange or yellow. A strong subvibrissal seta may or may not be present 

 (Fig. 4h) 15 



14 Male surstylar lobes evenly tapered in side view and curve inwards at the tips 

 in posterior view; cerci normal in size, clearly visible between the lobes and 

 reaching well below the middle of them (Fig. 3f). Anterior part of thorax with 

 very little pale or reddish colour, nearly all distinctly blackish-brown and lacking 

 metallic reflections. Costal cell darkened. Sternite 8 of female terminalia tapered 

 to a point (Fig. 5e) G. subnigra Drake 



— Lower part of the surstylar lobes evenly convex in posterior and lateral view, 

 leaving a narrow more or less parallel gap between them; cerci very small, 

 hardly reaching halfway down the lobes and scarcely projecting from between 

 them (Fig. 3d). Anterior part of the thorax often distinctly chestnut-coloured 

 with slight metallic reflections on the paler parts of the pleura. Costal cell almost 

 clear. Sternite 8 of female terminalia truncate with a transparent semicircular 

 extension (Fig. 5f) G. breviseta Czerny 



15 No strong subvibrissal seta; all are weak (Fig. 4i) G. angustipennis 



Zetterstedt 



— One subvibrissal seta is stronger than the others (Fig. 4h) G. apicalis 



(Meigen) and G. hendeli Czerny 



Opomyza florum (F., 1794). Only O. punctata can be confused with florum. It 

 is one of the largest of the British opomyzids. Its thorax, and often the abdomen, is 

 entirely yellow although there are often small brown lateral spots on the abdomen 



