2. DIALINEURA 585 



tliird to fifth or sixth segments ; eighth segment shining black or fulvous ; 

 pubescence all whitish yello-w until the eighth segment and even then partly- 

 yellow at the sides, fairly long and erect about the base but depressed and 

 short on the rest. Belly entirely obscured by pale grey dust, but the sides of 

 the abdomen are considerably revolute so that only about the middle three- 

 fifths of the belly can be readily observed ; hindraargins of the segments 

 narrowly yellow, or even orange on the end segments ; pubescence slight, pale, 

 and inconspicuous on the basal segments but becoming shorter and more 

 erect on the rest, and especially erect and rigid beneath the seventh segment. 

 Ovipositor fulvous, with the usual circlet of strong black spines, and with a 

 terminal pair of small brownish yellow pubescent rounded lamellae. 



Legs all orange except on the light yellowish grey coxas and the blackish 

 trochanters, and with the extreme tip of the tibiae and the gradually increas- 

 ing tips of the tarsal joints blackish. Pubescence practically absent (except 

 on the coxae), but the coxal spines almost as in the male though more con- 

 spicuous because of the shorter pubescence ; all the femora with dense short 

 closely adpressed scaly yellowish pubescence and with very minute sparse 

 black bristles all over, but the anterior femora with no strong bristles 

 beneath ; hind femora with the antero-ventral row of bristles irregular and 

 sometimes reduced to about five in number ; tibise and tarsi with bristles as 

 in the male but rather stronger and more numerous ; all the tibiae vsrith almost 

 dense minute black bristles all over. 



Wings almost as in the male, but rather more brownish and the veins very 

 conspicuous when seen from the tip of the wing. Squamae and halteres 

 almost as in the male. 



Length about 9 mm. 



This species does not vary much, and the male may be distinguished 

 from any other known European species of Theremdce by its combination 

 of bare face and hairy f rons ; the open fourth posterior cell, the silvery 

 abdomen of the male, the absence of any shining black frontal callus in 

 the female and the orange femora of the female place both sexes beyond 

 possibility of confusion. 



D. anilis appears to be common on sandhills on the coasts of Wales, 

 but I have no British records from elsewhere. I found it rather 

 common at Barmouth (in company with T. annulatci) in June, 1887, and 

 Colonel Yerbury look it freely at Porthcawl from May 3 to June 30. It 

 seemed to me that the male partly trusted to its silvery abdomen to 

 render it inconspicuous when flying over white sand, and that both sexes 

 imitated a Scatophaga when at rest; this imitation was emphasised by 

 their closing the wings closely over each other so that there were appar- 

 ently darkened cross-veins as in some species of Scutophaga. T. annnUda, 

 which was also common at the same time, appeared to trust its safety 

 entirely to its resemblance to the colour of the sand. It is possible that 

 Scatophaga may be distasteful to some enemy, because in the Syrphidce 

 Broichyopa hicolor also seems to mimic it for protection. Zetterstedt was 

 informed by Dahlbom that the female of Crabro patellatus kills the female 

 of D. anilis and stores its nest with it for the nutriment of its larvae. 

 Colonel Yerbury caught a male T. annulata in cop. with a female D. anilis 

 at Porthcawl on June 27, 1902. 



Synonymy. — Thereva rufipes Macq. is represented in the Paris Museum by a 

 female D. anilis and by a very rubbed specimen which may be T.fulva. Some 

 specimens of D. anilis in Dr P. B. Mason's collection were labelled T. pleheia. 



