278 LEPTID^. 



of the ovipositor is ratlier pale brown ; sidemargins all blackish. Belly 

 blackish or blackish brown with narrow yellow hindmargins, and in light 

 colored specimens with the basal segment (except on its middle) and the 

 broad sidemarginal hems yellow, or in still paler specimens the belly may 

 be more extensively yellow ; pubescence pale on the disc of the second 

 segment. 



Legs brownish yellow, but in dark specimens the hind femora have a 

 blackish dorsal blotch near the tip which runs back as a blackish streak 

 along the front and hind surfaces, and all the tarsi are blackish ; but in more 

 usual forms the bases of all the tarsi are Ijrownish yellow, and there is scarcely 

 any notable darkening on the hind femora or tibiae ; anterior cox» either dark 

 brownish grey, or in lighter specimens blackish grey with rather obscure luteous 

 markings, or greyish orange with a slight slaty tinge in front on the basal 

 half of the front pair and on all the front of the middle pair ; hind coxae 

 almost all slaty on the front and outer sides ; front coxae usually without 

 any traces of black hairs at the tip in front though sometimes Avith indications 

 of them, but the posterior coxae always with some black bristly hairs at the 

 tip in front ; trochanters blackish in dark, or obscurely orange in lighter, 

 specimens. 



Wings in strongly colored specimens with an obvious orange tinge which 

 becomes more conspicuous on the base and fore part and stigma. 



Length about 10 mm., varying from 8 mm. to 12 mm. 



This species (or form of L. tringaria) was distinguished by Loew in 

 1869 from Bavaria, and in typical specimens it certainly has a pecuHarly 

 distinct appearance, but as it has a strong tendency to vary towards 

 orange markings while L. tringaria has a tendency to vary towards 

 dark markings it is probably only a dark form of the latter. The darkest 

 forms of all are apparently much darker than those described by Loew as 

 X. nigriventris, and only a long series of specimens can indicate the gradual 

 change towards Z. ;!ri;i^7«ria; the darkest forms appear to be very local 

 in Britain, and I think that I have only seen them from Porthcawl in 

 Grlamorganshire, but dark forms of L. tringaria are very common in 

 Britain though apparently very rare on the continent; these forms 

 seem to belong to local races, as almost all specimens occurring to- 

 gether show a great similarity in coloration and size. The extreme forms 

 were first taken by Colonel Yerbury at Porthcawl in June 1903, but 

 in 1906 he made a special study of them at that locality and came to 

 the conclusion that no fixed boundary line could be drawn between the 

 darkest forms and L. tringaria ; an examination of his captures showed 

 about 20 per cent, which would pass as L. nigriventris, and nearly 

 40 per cent, more which might be light colored L. nigriventris, while 

 about 40 per cent, would range from dark to ordinary specimens of 

 L. tringaria, and about 2 per cent, would belong to the form vanellus. 

 L. nigriventris holds about the same position towards L. tringaria as L. 

 monficola does to L. lincola or as L. scolo^mcca does to Z. strigosa. 



L. nigriventris has occurred not uncommonly at Porthcawl in Glamorgan- 

 shire from June 4 to August 18, and the Eev. W. J. Wingate has taken 

 very similar specimens rather commonly at Hesledon in Durham, while 

 Colonel Yerbury took a male at Tarrington in Herefordshire. The female 

 has I believe never been previously noticed. 



Synonym)/. — In my list of British Diptera (KS8S) I introduced this species as 

 British, but my exponents of it were only some specimens of a small dark form of 

 L. trinfiaria which occurred near Barton Mills in Suflblk. The Rev. W. J. AVingate 

 recorded his specimens as L. compiciia Meig., but that species though allied is 

 perfectly distinct and has longer wings and a distinct stigma. 



