DURHAM DIPTERA. 1 33 



XXIV. 



59 (58). First antennal joint not long, fore and mid tibiae 



simple, wings with at most some small dark spots, 

 fore femora with short spines in the male. 



Hydrophorus, Whlbg. (244) 



60 (57). Fore femora neither thickened nor spined. 



Liancalus, Lw. (245) 



61 (1). Arista exactly terminal, that is exactly in the middle 



of the end of the third joint (III. 35-37). 



62 (75). Third antennal joint long, often very long, at least 



always longer than broad, conical (III. 36). 



63 (64). Proboscis bent in on the breast with a tooth at the 



end, acrostichal bristles absent. 



Aphrosylus, Wlk. (259) 



64 (63). Proboscis not bent in nor toothed. 



65 (66). Third antennal joint abruptly dilated at the base, 



then deeply cut out on the under side, palpi very 

 broad, hind coxae with a conspicuous blackish 

 bristle, acrostichal bristles in two rows. 

 239. Machterium, Hal. (1307. maritimce, Hal.) 



66 (65). Third antennal joint not cut out, but on both sides 



gradually narrowed to the point, palpi moderately 

 broad. 



67 (68). Abdomen compressed towards the tip, male organ 



long stalked and free. Systenus, Lw. (237|-) 



68 (67). Abdomen not. compressed, male organ not stalked 



and usually half sunk or hidden, with at most the 

 often thread-like lamellae apparent. 



69 (70). The second antennal joint produced thumb-like on 



the inside over the base of the third joint which it 

 seems to clutch, first antennal joint hairy on the 

 upper side (except in S. pallifies). 



Syntormon, Lw. (238) 



70 (69). The third antennal joint not produced thumb-like, 



first joint bare above. 



71 (74). Large robust species, 4-6 mm. Under half of the 



posterior orbit thickly haired. 



