586 . THEREVID^ 



3. PSILOCEPHALA. 



Psilocephala Zetterstedt, Ins. Lap., 526 (1837). 



Very closely allied to Thereva but with the frons of the 

 male and the face of both sexes quite bare (fig. 327). 



Pig. ZII .—Fsiloccphala ardea (J. x 33. 



Frons of the female narrower, without any shining black bare calli, 

 and bearing only very short sloping black bristly pubescence on the upper 

 two-thirds. Antennse with the basal joint about three times as long as 

 the second joint but not so long as the third. 



Thorax witli at most only very sliort decumbent pale thin pubescence and very 

 inconspicuous depressed sparse bristly black pubescence, but with the usual (or 

 more than usual) chsetotactic bristles ; pleura3 almost bare, but Avith slight pubescence 

 on the mesopleurse and the upper part of the sternopleurse, and with a dense rather 

 long tuft on the metapleur^. 



Abdomen with only sliort adherent pubescence. Genitalia of the male of a 

 different type to that of Thereva, as they are extended out conspicuously beyond 

 the seventh abdominal segment and are composed of at least a large covering dorsal 

 plate and large but shorter side lamella besides a complicated lot of internal 

 processes. 



Legs similar to those of Thereva, but the anterior femora bearing fewer bristles. 



Wings as in Thereva, and varying as to the fourth hindmarginal cell being closed, 

 contracted, or wide open, and often even differing in the sexes as to the cell being 

 closed (in the male) or slightly open (in the female). Squamse with only slight 

 fringes. 



Fsiloccphala contains only about seven European species, though five or 

 six more are Palsearctic ; about thirty-five are recorded from North 

 America and two from South Asia. 



1. P. ardea Fabricius. Frons of the male and face bare. Abdomen 

 of the male silvery white with the genitalia orange, of the female black 

 with white lateral spots. Wings tinged with yellow. Frons of the female 

 white in front but brown behind. 



Distinguished from the other British Therevidw in the male 

 by the bare frons and by the silvery abdomen with long con- 



