1930. 



267 



7. Middle thoracic stripe towards tlie front witli an elongato dark area attached 



to it on either side; scutelliim all yellowisli . . . .dilatata Strobl. 

 Middle thoracic stripe simple, well separated from the lateral stripes. 



8. 



8. Scutellum conspicuously darkened on each side . . . .maculata Mg. 

 Scutellum scarcely, if at all, darkened at the sides. 



sttbmacidata, sp. n, 



9. Bases of fork-cells not at all clouded rmhilipennis Curt. 



Bases of fork-cells conspicuously clouded nehulosa Mg. 



D. autumnal is (Mg.) Goet. — The original description of this 

 species is unrecognisable, but Goetghebuer gives a good figure of the 

 b^^popygium, and it will be well to follow hiiu in bis use of this name, 

 unless Meigen's species proves to be different on examination of the 

 type. The pale colour of the head will distinguish the species from all the 

 other British forms known at present, but D. serotina Mg. is very similar 

 and is likely to occuf with us ; according to Goetghebuer it diffei's only 

 in the details of structure of the bypop^^gium. I have taken D. autiun- 

 nalis in some numbers at Wood Walton Fen, Hunts, and there is a 

 male in the British Museum from Nairn {Yerburi/), determined by 

 Verrall as D. aestivalis. 



D. aestivalis Mg. — This species seems to be common, and is usually 

 recognisable by its predominant yellow colour, the head, however, being 

 blackish. It is distinctly the largest British species. There is some- 

 times a faint cloud over the r-;« cross-vein. This makes it just possible 

 that Meigen's D. maculata was this species, but I prefer to follow 

 Loew's interpretation. The specimens in the Yerrall collection labelled 

 D. a^Ji'iliiia are this species, but I consider Goetghebuer's identification 

 with D. aestivalis is probably correct. I do not know any JJritish 

 species which corresponds accurately to Meigen's description and tiji-ure 

 of D. aprilina. I have a male from Kneb worth, Herts, wliich is 

 identical in hypopygial structure with the other specimens of D. aesti- 

 valis examined, but differs somewhat in coloration, the pleurae being 

 largely dark, and the middle thoracic stripe much blacker and practi- 

 cally undivided. Goetghebuer's description would seem to have been 

 drawn up from a specimen of this darker form. 



D. laeta (Lw.) Goet. — The species which Goetghebuer describes 

 and figures under the name laeta Lw. may not be correctly named, since 

 Loew's original description stated that there were no dark patches 

 between the thoracic stripes, these being conspicuous in Belgian and 

 British examples. Goetghebuer's interpretation, however, may be 

 followed unless it can be proved erroneous after an examination of the 

 bypopygium of Loew's type. A possible earlier name for this species is 



2a2 



