1. THEREVA 579 



8. T. annulata Fal3ricius. Male entirely covered with silvery 

 pubescence; female without any shining black frontal callus. Halteres 

 whitish. Femora blackish in both sexes. Fourth posterior cell closed. 



A common and very distinct species. 



(J. Face and frons entirely covered with brilliant white tomentum, and 

 densely clothed with long pure white pubescence except on the upper part 

 of the frons and on the depressed middle part of the face ; this pubescence 

 slopes downwards on the sides of the face, and is conspicuously continued 

 quite as long and dense under the eyes (without a black hair being inter- 

 mixed) and ah round the back of the eyes ; face and frons slightly produced 

 in profile towards the base of the antennae, and when seen from in front 

 forming a broad bell-shaped space which is more than half the width of the 

 head ; the space below and behind the eyes fairly wide and still covered with 

 white tomentum but gradually diminishing in width as it ascends the back 

 of the head, and on the upper part with a row of (3-7) conspicuous rather 

 overhanging postocular black bristles, but no similar bristles occur on the 

 absolute back part of the head or if there are any they are very small and 

 difficult to detect ; vertex brownish, bearing moderately long forwards-sloping 

 black pubescence. Proboscis brownish, rather long and prominent though 

 thin ; palpi greyish white, bearing long upturned white pubescence. Eyes 

 quite bare, touching (or only linearly separated) for nearly one-third the 

 distance between the occiput and the antennae ; facets on the upper three- 

 fifths larger than these on the lower two-fifths. Antennse about as long as 

 the head, dull brownish black, but the two basal joints completely covered 

 with whitish dust and the third joint obscured ; basal joint long and 

 cylindrical, not at all incrassated, and bearing the usual circlet of (10-12) 

 black bristles round close to the tip but with long pure white pubescence on 

 the basal part ; second joint not a quarter the length of the first, and bearing 

 only a few very short sometimes black bristles ■ third joint about as long 

 as the first, and bearing at its tip a short thick bent-down style which is 

 terminated by an exceedingly short thread-like arista. 



Thorax with a dull greyish black ground colour on which two light 

 grey lines run down the disc and become a little widened where the 

 prsescutellar bristles occur, but everywhere obscured by abundant whitish 

 dust and almost white dense equal rather long nearly erect pubescence, 

 though this pubescence becomes faintly brownish white on the front 

 part of the disc (and in a specimen taken by Colonel Yerbury at 

 Porthcawl on May 23, 1903, obviously brown on all the disc), while the strong 

 black chsetotactic bristles stand out conspicuous ; pleurae with equally 

 abundant and rather longer quite white pubescence on a white dusted 

 ground colour. Bristles as in fig. 311 but usually with two pairs of prae- 

 scutellar bristles. Scutellum clothed with similar dust and pubescence to 

 that on_ the thorax, and with the usual two pairs of conspicuous slightly 

 converging black marginal bristles ; metanotum greyish white and quite bare 

 on the middle part, but with dense side tufts. 



Abdomen entirely covered with pure white almost silvery dust and 

 pubescence ; pubescence rather long but recumbent on the disc, though 

 long and outspread all downi the sides and nearly all equal in length ; all 

 the hairs long, silky, and pure white without a trace of a dark hair except 

 the black hairs connected with the genitalia. Belly covered with whitish 

 dust, but not enough to prevent the hindmargins of the segments being 

 yellowish ; pubescence long, but very thin and sparse. Genitalia dull orange, 

 beneath with a pair of thin incurved lamella which bear black bristly hairs 

 on their apical half, while the ventral hindmargin of the seventh abdominal 

 segment bears a fringe of black bristly hairs which are long at the sides 

 and are conspicuous from almost all points of view. 



Legs with the femora all dull blackish though very considerably obscured 

 by white scales ; tibiae dull yellow, except for the narrowly blackish tip ; 

 tarsi obscurely dull yellow about the base and after that obscurely dull 



