586 
DIP TEH A. 
5. Media not coalescing at anypoint with R 2 or R 3 . 
Cross vein present .. . . . . BoUtophilince. 
Media coalescing for some distance with R 2 or R a . 
Cross-vein absent. 
Antennae very long . . .. . . Macrocerince. 
Antennae short and flat .. . . . . Ceroplatince. 
Bibionidje. 
Medium sized ugly-looking flies. Antennce with 9-12 rather thick joints 
closely pressed together. Ocelli present. Front femora rather thick, 
front tibiae generally spined. Eyes of male close together or touching. 
Anterior veins thicker than the others. Wings often dark or with dark 
spots. 
These flies are easily recognised by their sluggish movements 
(though they have large wings), and by their colour being almost always 
either black or orange-red. In many species the male is black while the 
female is partly orange, as is also the case with some Mycetophilids 
(Sciarince). Their lazy habits and conspicuous colour-scheme suggest 
that the orange and black might represent in this case, as apparently in 
others, the “ warning colours ” of the distasteful and dangerous members 
of insect society, but no observations confirming this supposition 
appear to exist. 
The wings have conspicuous alulae. The sub-costa is generally rudi¬ 
mentary and the radius is often only two-branched. The flies might 
perhaps be confused with Mycetophilidce, since some of the latter are also 
black and orange, possess ocelli, and have often dark-coloured wings 
whose venation is not unlike that of a Bibionid. The two can be easily 
distinguished by looking at the antennae and the coxae of the legs, 
both of which are much longer in Mycetophilids than in Bibionids. 
The eyes in Bibio are divided (in the male flies) into two distinct 
upper and lower halves, separated by a narrow band. More or less well 
marked differences in the structure of different parts of the eye, usually in 
the size of the facets, occur in other flies. (Cf. Blepharocerids, Simuliids, 
Tabanids, Dolichopodids, Pipunculids.) Since, owing to the internal 
arrangements of facetted eyes, clearness of vision increases with the 
number of facets in the parts of the eye employed, we may suppose the 
sparsely-facetted areas to be used merely for the perception of com¬ 
paratively gross differences of light and shadow and of the motion 
