566 



THERE VID^ 



Legs varying moderately in the amount of obscure reddish orange on the 

 tarsi, and in the colour of the pubescence behind the anterior femora, as the 

 latter may be mainly greyish about the basal half of the front femora, while 

 the scaly yellow pubescence in front of the hind femora is at times much 

 more extensive or at other times very much restricted ; the black bristles 

 beneath the anterior femora vary in number, as there may be only one on the 

 front femora and only one or two on the middle femora, while the irregular 

 black bristles beneath the hind femora may vary in number from about eight 

 to twelve. 



Wings varying considerably in the intensity but not in the position of the 

 small cloudings, except that the clouding may occasionally be almost reduced 

 to the two cross-veins and the base of the radial fork, while on the other hand 

 the cloudings may be sharply marked though restricted, and rarely even the 

 base of the first posterior cell is clouded slightly brownish close against the 

 discal cross-vein ; the stigma may be brownish orange. Squamas sometimes 

 with dark brown margins. Halteres paler brown. 



All these variations may seem to be very slight, but they often tend 

 to cause uncertainty in distinguishing T. pleMia from T. nobilitata, and I 

 think it possible that an unrecognised species exists between T. pleheia 

 and T. hipundata. 



$ . Not at all like the male and but little variable, so that it can easily be dis- 

 tinguished from its allies. Frons broad at its narrowest part near the 

 vertex, more than a quarter the width of the head, and widening to more 

 than half at the antennae ; frons dusted brownish yellow, with an unusually 



large shining black callus (fig. 322), in front of which 

 are numerous fairly long black hairs extending 

 across (but not to the eyemargins) in a slight arc 

 but scarcely (if at all) extending down below the 

 antennae, while in front of them the pubescence is 

 black ; the callus is bare and impunctate, looped 

 up behind at the middle as far as the front ocellus 

 and notched anteriorly with a narrow yellow exten- 

 sion of the anterior frons, and almost always 

 reaching the eyemargins for its full width ; the 

 frons above the callus is dusted slightly darker 

 than anteriorly, and bears some rather sparse 

 shorter black hairs- face greyish white, clothed 

 with dense white or pale yellow pubescence, while similar pubescence extends 

 all over the jowls and lower half of the back of the head without a single 

 black hair intermixed except a distinct small clump of black hairs just 

 below the lowest part of the eyes ; back of the head pale greyish yellow, 

 but almost white on the lower part and (when seen from above) more 

 brownish yellow on the upper part, and the whitish lower part bearing dense 

 long white jmbescence which completely dies away about the middle of the 

 head, but is succeeded by slighter shorter inconspicuous brownish yellow 

 pubescence, while the usual scattered stout black bristles occur quite out on 

 the back part of the head, and the usual postocular ciliation of about fifteen 

 black bristles extends from the middle of the head to the tojj angle of the 

 eye, but only the top six or eight bristles are long enough to curve slightly 

 forwards. Eyes comparatively small. Antennae less pubescent about the 

 base than in the male ; third joint usually more decidedly brown. 



Thorax dull greyish dark brown, with two moderately distinct widely 

 separated brownish yellow stripes which extend the whole length of the 

 thorax, but which are somewhat vague and widened at eacli end and almost 

 widen to each other at the hinder end, amalgamating there with the similarly 

 colored hindmargin of the thorax ; sides of the dorsum more ashy, and the 

 pleurae more whitish grey. Pubescence on the disc composed of compara- 

 tively sparse but ubiquitous suberect short inconspicuous black hairs, which 



* In this lisure the frontal callus is somewhat foreshortened, or else it would appear to occupy more of the 

 frons, and the pubescence iu front of the callus is given as extending to the eyemargins. 



Fia. 322.- 



-Thereva plebeia ?. 

 X 16.* 



