DURHAM DIPTEIIA. 365 



LI. 637. 



28 (11). Third antennal joint orange, or at most only partly 



darkened. 



29 (32). Sternopleural spot always entirely black. 



30 (31). Third antennal joint large. {discicornis, Lw.) 



31 (32). Third antennal joint small. (didyma, Ztt.) 



32 (29). Sternopleural spot never entirely black, usually 



entirely pale. 



33 (36). Abdomen with a distinct black central stripe. 



34 (35). The vertical diameter of the eye longer than the half 



of the vertical diameter of the head, (divisa, Lw.) 



35 (34). Eye small, scarcely half as long as the head. 



(pallens, Lw.) 



36 (33). Abdomen without any black stripe. 



37 (42). Base of the abdomen with a distinct black dot on 



each side. 



38 (39). Vertical triangle without any black dot on its fore 



corner. gracilis, Mg. (2711) 



39 (38). Vertical triangle with a black dot on its fore corner. 



40 (41). Head more inflated than usual ; abdomen, in fresh 



specimens, without dark interrupted bands ; large 

 species, over 4 mm. {binotata, Lw.) 



41 (40). Head normal ; abdomen with dark interrupted bands 



or spots. {geminata, Mg.) 



42 (37). Abdomen with two dark places, but without any 



distinct black dots at its base. 



43 (44). Vertical triangle without any black spot at its fore 



corner ; dorsal stripes greyish black, seldom matt- 

 red in front. {hirsuta, Lw.) 



44 (43). Vertical triangle with a distinct black spot at its fore 



corner; dorsal stripes for the most part shining 

 red. ( 2 7°9- rufina, TAX..} 



637. Chlorops, Mg., &c. (Zetterstedt's Oscinus, part). 



The following table, taken from Zetterstedt and Loew, but 

 following a somewhat different plan from Loew's, may be 

 helpful in identifying these beautiful little flies. It includes 

 632. Centor, 633. Anthracophaga, 634. Haplegis, 



