Key (online version)

1a 
The bases of veins M_{1} and M_{2} arising from the discal cell at the same point, if a crossvein between them is present, then it is no more and 1/41/6 as long as the crossvein between M_{2} and M_{3} [Fig. 54]. Males holoptic [Fig. 39]. Distal part of R_{4+5} without dark marking. Male genitalia with basal ring that has a deep anteroventral concavity; hypoproct consisting of single, narrow lobe or of two lobes that are joint at the bases; claspers thin and Sshaped [Fig. 56]. 
subg. Anisopus Meigen 

2 
b 
Veins M_{1} and M_{2} arising separately from the discal cell, the distance between their bases at least 2/3 the length of the crossvein between M_{2} and M_{3} [Fig. 36]. Male holoptic or dichoptic. Distal part of R_{4+5} with dark marking of varying intensity. Basal ring of male genitalia without anteroventral concavity; hypoproct broad, either with or without shallow posterior concavity; claspers not developed [Fig. 28]. 
subg. Sylvicola Harris 

5 

2a 
Wing with dark band posterior of R_{2+3} [Fig. 49]. Hypoproct with two broad, fingerlike lobes [Fig. 48][Fig. 47]. 
S. (A.) punctatus (Fabricius, 1787) 


b 
Wing without dark marking posterior of R_{2+3} [Fig. 54]. Hypoproct differently shaped [Fig. 56][Fig. 42]. 

3 

3a 
Hypoproct with one pointed lobe; apex of gonocoxite with small oval plate that is beset with short setae [Fig. 56][Fig. 55]. Female frons almost as wide as eye width (5 : 6). 
S. (A.) fuscatoides Michelsen, 1999 


b 
Hypoproct with paired, apically tapering lobes; apex of gonocoxites with strongly sclerotized plate that is beset with long, golden setae [Fig. 42][Fig. 53]. Female frons distinctly narrower than eye (2 : 3). 

4 

4a 
Lobes of hypoproct rather slender and adjoining apically [Fig. 42][Fig. 40]; sclerotized plates on apices of gonocoxites with long internal projection, long golden setae only present on basal half and forming a tuft [Fig. 41]. [Female: Halters dark with pale knob. Wing with distance between R_{1} and R_{2+3} about twice as long as the distance between R_{2+3} and R_{4+5}; discal cell pointed. [Fig. 43]]. 
S. (A.) stackelbergi Krivosheina & Menzel, 1998 


b 
Lobes of hypoproct broader and shorter, apically somewhat diverging [Fig. 53][Fig. 52]; sclerotized plates on apices of gonocoxites without projection, simple, with rows of inwardly curved setae along its whole length, setae more or less forming a comb [Fig. 50]. [Female: Halters pale. Wing with distance between R_{1} and R_{2+3} about three times as long as the distance between R_{2+3} and R_{4+5}; discal cell truncate [Fig. 54].] 
S. (A.) fuscatus (Fabricius, 1775) 



5a 
Wing with weakly developed yellowish spots on the apex of R_{4+5} and in middle of cell r_{1}; wing membrane not darkened posterior of R_{2+3} [Fig. 18]. Eyes widely separated in males and females, frons slightly narrower than width of one eye. Gonostyles in male genitalia massive and broad; hypoproct broad and blunt apically, posterior margin almost straight and with pubescent lobes on anterolateral corners [Fig. 17]. 
S. (S.) limpidus (Edwards, 1923) 


b 
Wing with brownish spots on the apex of R_{4+5} and in the middle of cell r_{1} and otherwise with several distinct and indistinct dark spots [Fig. 15][Fig. 36]. 

6 

6a 
Wing strongly darkened apically and with two isolated pale spots (those in r_{2+3} and r_{4+5} are not contiguous) [Fig. 13]. Halters with blackish knob. Gonocoxites swollen apically and massive, almost rectangular in basal half, narrowed and lightly Scurved apically [Fig. 12]. 
S. (S.) suzukii (Matsumura, 1916) 


b 
Wing with pale spots in r_{2+3} and r_{4+5} contiguous or pale area larger and connected to pale areas posterior of R_{4+5} [Fig. 15]. 

7 

7a 
Dark apical spot in wing isolated and as a rule at most as long as the distance to the tip of R_{2+3}, posterior margin distinct or indistinct [Fig. 36][Fig. 10]. 

8 
b 
Dark apical spot usually without distinct posterior margin and connected posteriorly with the dark marking stretching across r_{1} and r_{2+3}, as a rule at least 1.5 time as long as the distance to the tip of R_{2+3}. Males holoptic. Distance between bases of M_{1} and M_{2} equal to or 1.5 as long as the distance between the bases of M_{2} and M_{3} [Fig. 15][Fig. 21]. 

11 

8a 
Males holoptic, frons no wider than one ommatidion [Fig. 39]. Gonostyles short. Apical spot of wing dark and distinct [Fig. 10]. [Median stripe on mesonotum reaching scutellum?] 

9 
b 
Males dichoptic, eyes widely separated. Gonostyles elongated. Apical spot of wing with indistinct posterior margin [Fig. 36]. [Median stripe on mesonotum not reaching scutellum?]. 

10 

9a 
Gonostyles almost rectangular at base and with narrow pointed posterolateral projection, parameres (claspers?) not visible; aedeagal guide broad and posterior margin is clearly not its narrowest part [Fig. 9]. 
S. (S.) zetterstedti (Edwards, 1923) 


b 
Gonostyles large, almost rectangular at base and with narrow truncate posterolateral projection; parameres well visible and with spoonlike apex; aedeagal guide less broad and gradually narrowing posteriorly [Fig. 37]. Female unknown. 
S. (S.) baechlii Haenni, 1997 



10a 
Hypoproct broadly rounded and with distal pubescent lobes; gonostyles massive and without laterobasal projection [Fig. 35]. [Distance between bases of M_{1} and M_{2} about equal to distance between the bases of M_{2} and M_{3}?] 
S. (S.) cinctus (Fabricius, 1787) 


b 
Hypoproct narrowed apically, with posterior emargination and with median pubescent lobes; gonostyles narrower and with short laterobasal projection [Fig. 28]. [Distance between bases of M_{1} and M_{2} about equal to 1.5 the distance between the bases of M_{2} and M_{3}?] 
S. (S.) fenestralis (Scopoli, 1763) 



11a 
Pale spot in r_{2+3} distinct and surrounded by well developed dark spots; apex of R_{2+3} completely darkened [Fig. 21]. Halters pale. Hypoproct massive, almost rectangular; gonostyles massive and trapezium shaped [Fig. 20]. 
S. (S.) japonicus (Matsumura, 1915) 


b 
Pale spot in r_{2+3} indistinct and surrounded by less distict dark markings; apex of R_{2+3} not darkened [Fig. 15]. Male halters with darkened knob. Hypoproct somewhat narrowed apically and with posterior emargination; gonostyles elongated and curved [Fig. 14]. 
S. (S.) matsumurai (Okada, 1935) 


