26 • BRITISH FLIES 



Mydaida:, as the lower outer veiiib do uol curve up and run 

 parallel with the hindmargin of the wing (except in a very 

 few species of Erax), but run out normally to the wing- 

 margin; upper branch of the discal vein ending long after 

 the wing-tip ; cubital fork long and not very wide open. 

 Vertical portion of the frons deeply sunken between the 

 protuberant eyes. Head well separated from the thorax by 

 a freely movable neck. Proboscis powerful, horny, and 

 without any fleshy labella, luit never elongated. Genitalia 

 usually conspicuous. Predaceous flies, with strong grasping 

 legs, which are armed with bristles especially on the tarsi. 



XII. ASILID^. 



Tlie AsiliJce are large to very large (but occasionally small) 

 powerful i)redaceous flies, known as the "Robber FYies," par excdlenir. 

 Tliey are not likely to be confounded with the species of any other 

 family, unless they might be with the Therevidcn or Apioceridw ; from 

 the Therevidie they may be distinguished by the protuberant eyes, 

 absence of soft furry pubescence, and longer subcostal vein, and from 

 the A]noce)'idce by the very distinct venation (with exceedingly few 

 exceptions), face, palpi, and antennae. The European species are very 

 numerous and many are very difficult to distinguish, but they have 

 been well worked out. 



24 (13) Anal cell short except in a few Empidce {Hyhotinm) and shorter 



than the preceding basal cell (when that is present), and the 

 upper basal cell rather long in the Em-pidce only; postical 

 vein with its lower branch recurrent (except in the Hylotince) 

 and its upper branch quickly lost in the discal vein ; cidjital 

 vein simple except in a few Empidce ; small cross-vein quite 

 absent; posterior cells apparently never more than four, but 

 usually less ; wing-veins altogether few and simple ; alula 

 obsolete. Face bare or only slightly pubescent in the MiCEO- 

 PHONA, but with peristomal bristles in Lonchopteridce and side 

 or genal bristles in Phoridce, but with no face-beard or 

 pubescence as in Asilidcc. Cephalic bristles usually strongly 

 developed. Species always small and distinctly chtetophorous. 



The four subsequent families become more and more bristly, and 

 may be distinguished from the Enekgopoda by their reduced venation, 

 in which there are never more than four and commonly only three 

 posterior cells, and in which the cubital vein is forked in only a feA\' 

 Emjndrt-. 



25 (30) Wing-veins (including cross-veins) fairly nonnal, or else the radial 



and cubital veins extended to almost the wing-tip. Antennae 

 with three (or rarely two) joints obvious, besides any style or 

 arista. 



26 (29) Wings rounded at the tip ; venation fairly normal, with the radial 



vein ending considerably l^efore the wing-tip, and with at least 

 one apparent cross-vein well out towards the middle of the 



