On the BoinlijH'nl Ftnnxi <>/' !*i<,nfli, Africa (Diptera). 73 



SUT.FAMILY USIINAE. 



CORSOMYZA. Wiedeinann (1820). 



Of this peculiar genus, very characteristic of the South African 

 Fauna, there are in the collection numerous specimens, representing 

 all the known species, with the addition of some new ones. The 

 special feature of the genus resides in the facial circular brush, which 

 consists of a dense pubescence of short hairs clothing the anterior part 

 of the frons and the whole face, which is surrounded by more rigid 

 and often differently coloured hairs. From this dense brush are 

 projecting on the upper side the antennae (the basal joints of which 

 are often clothed by a tuft of hairs of different colour), and below the 

 proboscis and. the long palpi. A similar conformation of the face is 

 to be found only in the North American genus Pantarbes, Osten 

 Sackeu, which, however, has a closed first posterior cell, and in the 

 Australian genus Lasioprosopa, Macquart. But this last genus, as 

 already stated by Schiner in the Novara work, is synonymous with 

 Corsomyza, its type species, Lasioprosopa bigotii, being Corsomyza 

 iiir/i-ipes, as confirmed by a specimen in the collection labelled under 

 this name by Bigot. 



The species in the collection are much alike in habitus and in the 

 colouring of the body fur ; they probably mimic Hymeuoptera, having 

 a very great resemblance to certain species of Osmia. They can be 

 distinguished as follows : 



1 (14). Third anteunal joint wholly black ; anal cell closed and usually pro- 



vided with a short stalk. 



2 (3). First auteimal joint elongate, as long as the half of the third, which 



is broad ; base of the antennae pale-haired ; face yellow, with the 

 circular brush not marginated with black ; tibiae and tarsi red. 



simplex, Wied. 



3 (2) First autennal joint short, always shorter than the half of the third. 



4 (o) Hind tibiae densely feathered with very long black hairs ; face yellow, 



the circular brush not marginated with black hairs ; antennae 

 with the first joint pale-haired and the third joint broad. 



pcniiipes, Wied. 



5 (4) Hind tibiae not densely feathered, sometimes only thinly ciliated. 

 I) (13) Facial brush formed by whitish or pale yellowish hairs. 



7 (S) First antennal joint clothed on the upper side with black hairs, which 



form a striking black tuft within the brush ; this last is surrounded 

 with dense black hairs. Tibiae and tarsi black ; third antennal joint 

 narrow, but a little dilated at end . . niyripes, Wied. 



8 (7). First anteunal joint with yellowish or whitish hairs; third auteuual 



joint filiform and much dilated at end. 



