ASILIN^ 625 



exceedingly thickened; middle tibiae armed with a very strong blunt 

 terminal thorn. 



2. Asi/iis. Antennal style bare and slender, with its first joint much 

 shorter than the second ; middle tibise without a terminal thorn. 



3. Ommatius. The bristle-like antennal style with comb-like hairs on 

 the underside. 



Several genera had previously been proposed by Macquart on rather 

 vague characters. 



Loew then divided the European Asilincc into a number of smaller 

 groups to which in those days he hardly dared to give the rank of genera, 

 but, in accordance with the general trend of scientific nomenclature and 

 the test of experience, all his groups have been accepted by most sub- 

 sequent writers as good genera, and many additional ones have since 

 been distinguished ; Schiner only undecidedly acknowledged these genera 

 in 1862, but accepted them all without hesitation when he dealt with the 

 Asilidce of the world in 1866, and Loew himself to the end of his days 

 defended the retention of all of them. In Britain we have only Loew's 

 " super-genus " Asilus to deal with, and it may be contended that these 

 smaller genera provide a separate genus for almost each one of our native 

 species, but an examination will show that several of these smaller genera 

 contain from twenty to thirty European species. 



Loew in 1860 (Die Dipteren-Fauna Sildafrika's, p. 142) wrote " The 

 " number of species belonging here is already so great, the difficulty of clearly 

 " distinguishing them is so serious, and the task of recognisably describing 

 " them is so difficult, that their separation into a larger number of genera is 

 " absolutely necessary. ... If the number of species in one genus has so 

 " accumulated, as in the Meigen -Wiedemann genus Asilus, which already 

 " contains at least 500 described species, if these species are so closely 

 " allied that the most exact details on precise but little obvious plastic 

 " distinctions are indispensable for their recognition and apparent 

 " grouping, if thereby the experience is continually repeated that new 

 " species are published without every consideration of these details and 

 " that determination from the descriptions given is an almost absolute 

 " impossibility, then it is surely the right time to found smaller genera 

 " on those characters and so to enforce the necessary attention to those 

 " plastic characters, for the advantage of scientific progress and the 

 " checking of the ever increasing confusion. If no distinctions offer 

 " themselves so material as in other genera, less material ones must be 

 " used ; if they are only so chosen that true allies are not separated from 

 " each other, then such genera should not be censured ; if on the other 

 " hand it can be shown that the choice of other distinctive characters 

 •' would have led to more precise and more easy distinction, or to genera 

 " which would correspond better with the natural grouping of the species, 



2 R 



