1. THEREVA 567 



overtop the more conspicuous short adpressed brownisli yellow hairs ; this 

 brownish yellow pubescence is slightly longer and more greyish tinted about 

 the sides of the dorsum ; pleurae with fairly abundant long greyish white 

 pubescence, which forms the usual dense long tufts on the back part of the 

 mesopleurse and on the metapleurae ; none of the pubescence on the dorsum 

 or on the pleurae is quite dense enough to conceal the ground colour ; prae- 

 scutellar bristles occasionally in two pairs. Scutellum greyish yellow, with 

 rather longer though still inconspicuous black hairs and with depressed 

 yellowish pubescence. 



Abdomen black with the hind part of each segment yellowish ashy grey, 

 usually dull on the black parts though sometimes shining ; hindmarginal hem 

 of the second segment often fairly broad and conspicuously pale yellow but 

 occasionally orange, while the hems on the next two segments are very 

 narrow, and sometimes a pale hem is just visible on the fifth hindmargin, 

 or in a large specimen (Wendover, June 9, 1899) the second, third, and fourth 

 segments all have narrow orange hems ; basal segment greyish black ; next 

 three segments each black with a light ashy grey (slightly yellowish) hind- 

 margin (before the pale hindmarginal hem) which occupies about a quarter 

 of the segment at the middle but widens outwards until it occupies about 

 half of the sideraargins, and the basal corners of the second segment obscurely 

 light grey ; fifth and sixth segments usually almost all ashy grey, but some- 

 times the fifth segment with a comparatively large part of its base and the 

 sixth segment with a narrow portion darkened and both with the actual 

 base shining black, or both may have a fairly broad shining black base ; 

 seventh and eighth segments shining black, but the seventh segment may 

 be slightly dusted with grey at the extreme sides and hindmargin ; base 

 of the ovipositor blackish chestnut and the ring of spines dark red, while 

 the apical lamellae are short semicircular and clothed with dense short rigid 

 bristles. Pubescence on the black parts of the second and third segments 

 all very short and black, adpressed and very inconspicuous, but on the sides 

 of the greyish part of those segments greyish white, and conspicuous though 

 hardly forming a hindmarginal fringe, on all the basal segment greyish white 

 and forming a conspicuous long fringe all across the hindmargin ; the fourth 

 to eighth segments bear all over rigid little black bristles, but a few short 

 depressed pale hairs may be intermixed about the basal part of the fourth 

 segment. Belly blackish ashy grey with broad obscurely greyish yellow hind- 

 marginal hems to the second and third segments and a narrow hem to the 

 fourth segment, all of which meet the corresponding dorsal hems ; pubescence 

 long and thin, though rather sparse and inconspicuous on the three basal 

 segments, and on the other segments composed of rigid little black bristles 

 which however are less dense on the fourth segment than on the others. 



Legs colored as in the male, but the pubescence on the femora much 

 slighter, shorter, and less conspicuous, and usually greyish white behind the 

 front femora but sometimes ^vith numerous black hairs near the tip ; the 

 still slighter pubescence behind the middle femora whitish with rarely 

 one or two black hairs intermixed ; all the femora bear almost all over a 

 whitish adpressed almost scaly pubescence. Bristles beneath the front 

 femora usually two, beneath the middle about five, and beneath the hind 

 pair about nine placed irregularly. 



Wings almost as in the male, but sometimes cloudings are visible at the 

 usual places on the cross-veins, on the basal piece of the upper branch of 

 the postical fork, on the veins ending the discal cell, and at the radial fork. 

 Squamae more hyaline, with a brownish yellow margin and brownish grey 

 fringes which are rather short and coarse on the outer part but long thin- 

 haired and straggly on the inner part. Halteres blackish brown, with the 

 stem paler. 



Length about 10-5 mm. 



This species varies in many details beyond what has been mentioned 

 above. Two males from Padstow may belong to a distinct species which 

 would come between T. plcheia and T. hijjinidata, but at present I consider 

 them to be only varieties of T. plebeia which have numerous black hairs 



