ON THE BRITISH SPECIES OF SIMULIUM. 



27 



Classification. 



The British species of Simulium fall readily into two groups, which may be defined 

 as follows : — 



Group A. — Tibiae of the front and middle legs with a large patch of silvery-grey 

 dusting on the front or outer side ; legs and abdomen with very fine hair-like pubes- 

 cence ; thorax and abdomen of the male usually with silvery markings ; last three 

 abdominal segments of the female shining ; front tarsi more or less thickened ; 

 halteres always light yellow ; male genital claspers flattened dorso-ventrally. 



Group B. — Tibiae without any silvery-grey dusting ; if the front tibiae sometimes 

 appear silvery, this is owing to the colour of the pubescence ; legs and abdomen 

 more or less densely clothed with a coarse close-lying pubescence, which is almost 

 scale-like and usually yellowish or golden ; thorax and abdomen of the male without 

 silvery markings ; abdominal integument of the female entirely dull ; front tarsi 

 not at all thickened ; halteres often dark ; male genital claspers diverse in form^ 

 but never flattened dorso-ventrally and usually roundish in section. 



Group A. 

 Table of males. 

 Hind tibiae and metatarsi conspicuously pale on the basal half 

 Hind tibiae pale only at the extreme base, if at all 

 Front metatarsi about 6| times as long as broad 



Front metatarsi about 5 times as long as broad 



3. Hind metatarsi mainly dark and more or less thickened 

 Hind metatarsi largely pale and not at all thickened . . 



4. Middle tibiae conspicuously yellowish or silvery on the basal third or 



half 



Middle tibiae entirely or almost entirely black (for distinctions between 

 these three species see figures of genitalia) . . tuberosum, morsitans 



2 



a 



ornatum 

 variegatum 

 4 

 argyreaium 



reptans 



austeni 



Table of females. 



1. Frons greyish, dull . . . . . . . . . . . . . . . . 2 



Frons blackish, shining . . . . . . . . . . . . . . . . 5 



2 . Fore and mid femora darkened on the apical half . . . . . . ornatum 



Fore and mid femora entirely or almost entirely yellow . . . . variegatum 



3. Face dull greyish . . . . . . . . . . . . . . . . . . 4 



Face shining blackish like the frons . . . . . . . . . . tuberosum 



4. Thorax somewhat shining, with scarcely a trace of silvery-grey lateral 



patches towards the front . . . . . . . . . . . . argyreatum 



Thorax scarcely shining, with coarser pubescence and fairly distinct 



silvery-grey lateral patches towards the front . . . . . . . . 5 



5. Pale markings of legs sharply defined ; hind metatarsi clear yellow on 



the basal half . . . . . . . . . . . . . . . . reptaiis 



Pale markings of legs less sharply defined ; basal half of hind meta- 

 tarsus more smoky yellow . . . . . . . . . . . . . . 6 



6. Abdomen distinctly yellow at the base* . . . . . . . . morsitans 



Abdomen not yellow at the base* . . . . . . . . . . austeni 



♦This is only a doubtful distinction, as I have seen only one female which can with 

 any reasonable certainty be associated with the males described as S. austeni. 



