1. THEREVA 565 



the small piece of the postical vein between the small cross-vein and its own 

 fork the discal vein above the upper outer angle of the discal cell, and very 

 slightly at the base of the radial fork ; stigma rather conspicuously brownish 

 orange. Squamse (alar) smoky yellowish glassy, with pale brownish yellow 

 margins and slight obscure yellow fringes. Halteres blackish brown, with 

 the stem rather paler. 



Such a specimen would be easily distinguished from T. noUlitata by 

 its blackish hue and the well- contrasted pubescence on the dorsal and 

 ventral surfaces of the abdomen, as well as by the pale pubescence having 

 in general a' more greyish hue; but T. pleUia varies as follows: 



Face lighter ashy grey with a slight brownish tinge on the upper part and 

 on the upper part of the back of the head, and the pale pubescence on the 

 face of a more pale brownish yellow tint (in a specimen possibly not con- 

 specific taken at Padstow in July, 1902, numerous black hairs are intermixed 

 on the face) • frons equally pale greyish brown all over ; lower part of the 

 back of the head with the pubescence well away from the eyes more exten- 

 sively pale, and at the same time the black pubescence on the frons and 

 face more extended (also Malvern Hills, but on June 8, 1902) ; vertex covered 

 with light grey dust. 



Thorax brownish and with the shorter yellow pubescence abundant, con- 

 spicuous, and equally distributed all over ; or on the other hand ashy brownish 

 with the shorter pubescence nowhere abundant but more blackish or only 

 comparatively inconspicuous light brownish grey ; pleurae with the ordinary 

 pubescence paler or. even whitish grey without any trace of yellow or fulvous, 

 and the mesopleural tuft sometimes more greyish yellow and almost without 

 black hairs, and the metapleural tuft at the same time composed of orange 

 yellow hairs with a fairly conspicuous back fringe of black hairs on the ujjper 

 part, or sometimes the pleural tufts (especially the metapleural one) mainly 



black haired. i • i j i 



Abdomen with the pale hindmarginal hems varying very much m breadth 

 and intensity, being sometimes equal and rather broad on the second and 

 third segments, or at other times narrow and equal on the second and next 

 two segments, while often the fifth segment has no hem, or the hems may 

 continue to the sixth segment ; the hems are usually pale yellow but may be 

 brownish orange, or even glaring white on the second and third segments and 

 obscure on the others ; the ashy grey bands also vary in colour towards 

 having a strong brownish tinge or even sometimes almost blackish, m which 

 latter case they are less distinct and tend to merge into the black basal part of 

 the segments and become less widened towards the sides, and sometimes the 

 ashy grey bands are much narrower (Malvern Hills, June 8, 1902) and the 

 black ground colour very extended (Gravesend, June 11, 1898); sometimes 

 the brownish ashy grey bands are so extended as to cause the black colour to be 

 reduced to the base and middle quarter of the second segment (as is usual m 

 T. nohilitata), to the middle two-thirds of the base of the third segment 

 extending about half-way down the segment, and to the middle half of the 

 base of the fourth segment for about half-way down the segment (Aberlady, 

 June 23, 1884); the basal plate of the genitaha which looks like an eighth 

 segment is seldom visible. Pubescence varying in the greater or less sharp 

 distinction between its colour on the dorsal and ventral parts; the ventral 

 brownish yellow hairs sometimes extending upwards gradually round the 

 sides, or on the other hand the ventral pubescence sometimes dull whitish. 

 Belly varying from blackish grey through brownish ashy grey to lighter ashy 

 grey, and its pale hindmarginal hems sometimes narrow and inconspicuous 

 except on the third segment ; the narrow lateral pale hem may extend the 

 whole length of the abdomen or may be entirely absent. Genitalia^ with the 

 dorsal and lateral plates varying from greyish black to dull reddish brown 

 and the pubescence on them less contrasted in colour, as it may beless black 

 about the base of the lateral plates and less tawny on the long hairs on the 

 hind part, while the ciliation across the hindmargin of the last ventral 

 segment may he merged into the general pubescence of the segment. 



