﻿On tlie BoiiibyliiiJ Fauna of South Africa {Dipfera). 7 



4 (3). Hairs mostly of yellowish or greyish colour, the black hairs on 

 abdomen veiy scarce and limited to the sides or apex ; no distinct 

 silvery spots, or very rarely small ones on the frons alone. 



minor Group. 



i) (2). Eyes of the male sepai-ated, head and fore part of thorax provided 

 with strong- bristles ; third antennal joint long and very attenuate ; 

 pixlvilli very small, almost wanting-; wings with a broad basal 

 comb and with the discoidal cell very obtuse outwardly, almost 

 truncates . ..... m leans Ofroup. 



() (1). Hind femora not spinose at base, with long hairs only; antennae 

 rather distant at base, with the first joint distinctly thickened ; 

 wings with no distinct basal comb . . . senex Group. 



(A) Group of B. ater. 



ill this group are included the species which have united eyes in tlie 

 male and a narrow frons in the female, no strong bristles on the fore 

 part of the thorax, and hind femora with strong bristles underneath 

 near the liase. They may be at once distinguished by the prevalent 

 black colour of the dense furry pubescence under which are very 

 distinct spots of silvery scales. 



This group, however, is a very artificial one, and the following 

 species may be divided at least in three natural series: (1) that of 

 B. lateralis — that is to say, the gen. Triplasins \ (2) that of B. analis 

 (No. 2); and (8) that of B. ornaf'is (No. o to No. 7). The known 

 South African s[)ecies may be distinguished as follows : 



1 (4). Thorax on each side with a broad and complete whitish stripe ; frons 



of female with numerous, long and partly bristly hairs ; wings with 

 the basal comb long but formed by very thin bristles ; they are 

 blackish on the fore half, and hyaline with black spots on the posterior 

 half ; second longitudinal vein rather strongly looped at end. 



2 (3). Three submarginal cells usually jn-esent ; the dark spots on the hind 



half of wings more numerous anii confluent . hivitattus, Loew. 



3 (2). Only two submarginal cells present ; hind half of wings with only four 



round and isolated dark spots . . . lateralis, Fabr. 



4 (1). Thorax void of whitish lateral stripes: wings without isolated dark 



spots ; second longitudinal vein less looped at end. 

 .") (lo). The black patch at the base of the wings extending to the discal 



cross- vein ; alula very long and narrow, black. 

 ») (7). Wings with the basal half equally black, the apical half hyaline; 



first posterior cell broad and briefly stalked ; squamae provided with 



a silvery fringe ; thorax with yellowish hairs in front. 



argentatus. Fabr. 

 7 It)). Wings with the basal black patch limited to the fore part, the anal 



and axillary cells being in part hyaline ; first posterior cell narrow, 



and long-stalked ; squamae with a black fringe : thorax with entirely 



black hairs in front. 



