578 THEREVID^ 



with an equally large but ratlaer less defined dark arc; fiftli segment with 

 only an elongate oblong blackish space on more than the middle half of the 

 foremargin which does not extend half-way down the segment ; fifth and sixth 

 segments each with a narrow dark brown hindmargin ; pubescence longer and 

 more erect about the sides of the three basal segments, whitish and recumbent 

 on the silvery grey parts of the second and third segments, but very incon- 

 spicuous and dark brown on the dark parts; on the rest the black stubby 

 pubescence is as in T. anmdata. Belly wider, all covered with whitish grey 

 dust; second and third segments with a fairly wide but inconspicuous 

 yellowish _ hindmargin, and the next two segments with a narrow yellow 

 hindmargin ; pubescence on the three basal segments all slight short depressed 

 and pale, but on the next four segments rigid and black. 



Legs much as in T. annidata, but the tibial bristles on all legs and 

 the apical circlet on the front pair much stronger ; coxae almost silvery white, 

 with _ snow - white pubescence, and with the black bristles conspicuous ; 

 anterior femora without any bristles beneath in the Rannoch specimen, but 

 with one or two strong bristles about the middle in the Nethy Bridge 

 specimens and with one bristle behind nearer the base. 



¥iQ.Z'ii.—Thcrcvaliin%data'i. x 9. 



Wings (fig. 324) perhaps rather more hyaline or without the slight yellowish 

 tint which occurs in T. anmdata; fourth posterior cell nearly always wide 

 open, but sometimes only moderately so. Halteres blackish, with just the top 

 of the knob and the base of the stem rather pale brown. 



Length 9-5 mm. 



This species might easily be mistaken for T. annulata, but the open 

 fourth posterior cell gives a good (though variable) distinctive character ; 

 it may moreover be easily distinguished by the blackish halteres, erect 

 blackish pubescence on the thorax, and in the female by the extensive 

 blackish brown cross-bands on the abdomen. It is curious that w^hen 

 Zetterstedt enumerated (Dipt. Scand., xii., 4586) ten species of Tliereva 

 with a closed fourth posterior cell he omitted to mention T. luimdata, 

 though he said " nostratum tantum in Tli. anili eadem area aperta occurrit." 



T. lunukita first became known to me from a female taken by Colonel 

 Yerbury at Kannoch in Perthshire on June 24, 1898, and it was not until 

 1906 that I came to the conclusion that it must belong to this little known 

 species ; soon afterwards however I detected two more females in rather bad 

 condition among his captures at Nethy Bridge in Inverness on June 25, 

 1905 ; then in 1906 Messrs D. Sharp and C. G. Lamb found it in fair numbers 

 at Nethy Bridge on the rough stony ground by the edges of water channels 

 which had partly dried up in the summer, but all the captors state that the 

 specimens are exceedingly difficult to catch. It has previously been recorded 

 from only extreme North Europe, where it is apparently not uncommon. 



Synonymy. — I have seen the specimens in Zetterstedt's collection at Lund (3 S , 

 3 ? ) which all have the fourth posterior cell more or less open, though one male has 

 it only narrowly open. It can hardly be T. cctsia Meig. because that has " 8ch winger 

 Weiss." 



