264 DURHAM DIPTERA. 



XXXIII. 459. 



18 (19). Eyes distinctly separated ; hinder side of mid tibiae 



with usually only two bristles ; inner fore side of 

 hind tibiae with from two to three bristles ; squamae 

 whitish. 



2025. Hydrotcea dentipes, F. 

 Very common. 



19 (18). Eyes only divided by a very fine line ; mid tibiae 



usually with four bristles behind ; inner fore side of 

 hind tibiae, from middle to tip, with a row of long 

 bristles; squamae yellowish. (2026. similis, Mde.) 



20 (13). Eyes narrowly touching. 



21 (22) (25) Middle of the hind femora beneath with two 



erect bristles. (2032. albipitncta, Ztt.) 



22 (21) (25). Hind femora beneath with one bristle. 



23 (24). Hind tibiae inner side with one strong bristle, which 



is bent at the point. (scambus, Ztt.) 



24 (23). Hind tibiae inner side with a tuft of numerous 



bristles. (2031. armipes, Fin.) 



25 (21) (22). Hind femora beneath without bristles. 



26 (27). Hind femora much bent ; hind tibiae middle of inner 



side with a tuft of several close-lying bristles. 



{pandellei, Stein) 



27 (26). Hind femora straight, or only slightly bent; hind 



tibiae without a tuft on inner side. 



28 (29). Mid tibiae, besides the hinder bristles, with an inner 



hind bristle ; V.4 4 at most only a little longer 

 than V.4 3 . (2028. militaris, Mg.=impexa, Lw.) 



29 (28). Mid tibiae without inner bristles ; V.4 4 nearly twice as 



long as V.4 3 . 



30 (33). Outer fore side of mid tibiae about the beginning of 



the last third with distinct bristles. 



31 (32). Abdomen shining blue, with a narrow dorsal line 



when viewed from behind. {bispinosa, Ztt.) 



32 (31). Abdomen black, with a broad dorsal line and broad 



hind-marginal bands on segments two and three. 



(2027^. pilipes, Stein) 



