306 Mr. J. E. Collin's Contribution towards knowledge of 



or highly chitinised. Legs in Palaearctic species never partly 

 yellow. Ungues and pulvilli long in the male, but never so in the 

 female. Female front tarsi never dilated. Wings with the anal 

 vein continued, even if faintly, to the wing-margin, and costa 

 extending to end of discal vein. Practically no distinct spines at 

 mediastinal break in costa. Postical cross-vein usually distinctly 

 oblique and often sinuate. Radial and cubital veins sometimes 

 slightly converging towards the tip. Thoracal squamae never very 

 conspicuously larger than the alar squamae, often much smaller. 



The two genera into which this group is at present 

 divided may be distinguished as follows : — 



1. (2) Arista distinctly pubescent or even plumose. Females with 



eyes widely separated and true orbital bristles present 

 (even if small), the front pair pointing forwards. 



Hammomyia Rond. 



2. (1) Arista bare or microscopically pubescent. Females with 



eyes approximated as in the males, or if somewhat 

 separated, the orbital bristles absent. Hylephila Rond. 



Hylemyia grisea Fin., and Choiiophila albescens Zett., of 

 the British List belong to the first genus. CJiortophila 

 buccata Fin., and unilineata Zett., to the second. Outside 

 Europe species of both genera are known to occur in 

 North and South America. 



The species of Hylephila are superficially remarkably 

 alike, and consequently mistakes in identification have 

 been frequent. Further confusion has been caused by the 

 females having been mistaken for males owing to the 

 similar approximation of the eyes on the frons in both 

 sexes. The most certain method of identifying the males 

 is by an examination of the genital organs, and Schnabl 

 must be given the credit for being the first to illustrate 

 the remarkable specific difTerences exhibited by these 

 organs. Unfortunately in some cases his identifications 

 were wrong, while his figures fail to give a good idea of 

 the excellent characters to be found in the structure of 

 the aedeagus. To remedy this defect fresh figures have 

 been prepared, and the writer has pleasure in gratefully 

 acknowledging the help he has received from Dr. J. 

 Villeneuve of Rambouillet in the loan and gift of specimens 

 for this purpose. 



