2. ONCODES 463 



4 (3) Squamfe with blackened margins. 



5 (6) Femora black at the base. zo7iatus Erichs. 



6 (5) Femora all yellow (or at least all one colour). 



7 (8) Blackish species. 2 pallipcs Latr. 



{nigripes Zett. ?) 



8 (7) Yellow species. formosus Loew. 



0. etruscus Griff, is probably a variety of one of these species, but it 

 is at present difficult to say which; it has the wings brownish tinged, 

 and the femora black at the extreme base. 



0. puhescens Latr. "Pattes blanchatres" was queried by Latreille 

 himself as a synonym of " Syrphtis orbimlus Fab.," which in turn is almost 

 certainly a synonym of Acrocera globulus. 



0. nigripes Zett. according to a female in Kowarz's collection from 

 Pontresina may be distinct, as it has the frons conspicuously covered with 

 pale down and the thorax more coarsely punctate; legs black with just 

 the tip of the femora yellow, tibia brown or dark brown ; and the squamee 

 whitish with the margin blackish in front but light brown behind. 



The genus is represented by about ten species from North and Central 

 America, one from South Africa, one from South Asia, and about six from 

 Australia and New Zealand. 



1. O. gibbosus Linne. Squamse bone-white, with hardly darker 

 margins. Halteres orange or brownish. "Wings with the foremarginal 

 veins pale yellowish, but with no dark clouding. Femora mainly black. 



A remarkably gibbous fly, with bone-white markings on 

 the abdomen which are restricted in the female to the narrow 

 hindmargins of the segments. 



<^. Head (figs. 265, 268) small, almost globular except for being a little 

 flattened behind and beneath. The enormous eyes occupy almost the 

 whole head except the vertex and the small concealed face; face and 

 frons almost on the underside of the head and forming a nearly equila- 

 teral triangle of which the dull velvety frons occupies the upper half, 

 but sometimes the frons is dull black with slight grey tomentum; 

 frons quite bare and with slightly raised margins which slope gradually 

 down inwards so as to leave a broad middle channel. Face very short, 

 dull l)rown, extending down the sides of the mouth ; jowls small but 

 distinct, deep black and bearing some fine pubescence on the back part; 

 lower part of the sides of the mouth also deep black and not quite bare ; 

 back of the head dull blackish, narrow but visible all the way up, and bearing 

 inconspicuous brownish or yellowish brown pubescence ; ocellar space raised, 

 shining black, with two gleaming red ocehi. Eyes enormous, quite bare ; 

 facets all equal, but a channel runs from the back part about half-way across 

 the middle of the eye. Antennae blackish brown, very small and short ; 

 basal joint so minute that the antennae have often been called two-jointed ; 

 third joint distinctly transverse and bearing a subterminal arista ; arista 

 swollen and polished black at the base but becoming thinner (though not very 

 thin) and brown or even pale brown and appearing to be thicker near its end 

 than just after about its base, while the actual tip bears a minute apical 

 bristle ; arista longer than the antennae. 



Thorax shining black with a slight brownish aeneous tinge, and clothed 

 with rather thick brownish yellow, greyish yellow, or greyish pubescence 

 which slightly obscures the ground colour ; this pubescence is rather depressed 



