Didea. 251 



raarkings on abdomen Eyes sparingly and short-haired; the upper 

 facets, towards the suture, a little enlarged in the male, Ocellar triangle 

 rather large and elongate. Antennæ well above the middle, somewhat 

 porrected, the third joint elongated, about twice as long as the two 

 basal together, somewhat attenuated towards the apex. Arista ap- 

 parently bare. Epistoma yellow, with or without a short, black middle 

 line, hairy, with a slightly protruding central knob ; mouth edge retre- 

 ating; jowls alniost not descending, The mouth parts resemble those 

 in Syrphus; clypeus with a large basal part; proboscis rather short 

 and stout; palpi short, Scutellum brownish or yellow, without fringe 

 below the margin, only with short hairs just at the margin. No 

 bristles on thorax or scutellum. Abdomen ovate, considerably broader 

 than thorax, rather flattened; it has a distinct, somewhat raised margin 

 (as in some species of Syrphus); there are three, or sometimes in the 

 female four greenish or yellow bands, the first interrupted and some- 

 times also the third and fourth. In the male there are, as in SyrphuSr 

 five not transformed dorsal segments; on the ventral side there are 

 hkewise five normal segments, but the fifth is partly hidden under 

 the genitalia so that it looks as if it is unsymmetrical. The genitalia 

 are rather large, the sixth to ninth segments distinctly seen on the 

 ventral side. In the female there are likewise five normal abdominal 

 segments, but generally three small segments more are visible, at all 

 events above. Legs with the hind tibiæ a little dilated in the middle, 

 and below the middle a little incurved on the posterior side; tarsi 

 with the four last joints flattened. Wings with a deep loop on the 

 cubital vein above the first posterior cell. Thoracai squamula besides 

 the marginal fringe of long, branched hairs also with long hairs on 

 both sides, at all events towards the margin. 



The genus is, as said, nearly related to Syrphus ; it is distinguished 

 especially by the loop of the cubital vein, which, to be sure, is present 

 also in a few species of Syrphus, but less pronounced; further the 

 antennæ are rather long with the third joint elongate, and the ab- 

 domen is flat, with a distinct, raised margin (a similar shape of 

 abdomen is also present in some species of Syrphus); also there 

 is no fringe of downwards directed hairs below the margin of 

 scutellum. 



The developmental stages are not known ; Verrall suggests, no 

 doubt correctly, that the larvæ are aphidiphagous, because D. inter- 

 media was found on bushes of Ulex infested with an Aphis; the same 

 author records that a specimen (possibly type) of D. fasciata Macq, 

 in the Paris Museum was a bred specimen, but without any particulars 

 given. 



