42 



Thriamheutes, and Silvius. Of these, Pronopes, Hinea, and 

 Thriambeutes are African genera, each of which at present includes 

 but a single species, while seven species of the widely distributed 

 genus Silvius have been described as occurring in the Ethiopian 

 Region. Recently the " subgenus " Subpangonia, Surcouf, has 

 been described* for a new species, the type of which was taken in 

 West Africa, near the frontier between French Congo and Cameroon. 



Genus CHRYSOPS, Meigen. 



Nouvelle classification des mouches a deux ailes (Diptera L.), p. 23 

 (1800) : Illiger's Magazin fur Insektenkunde, Bd. II., p. 267 



(1803). 



Plate II., and Plate III., fig. 17. 



Some seventeen species of this widely-distributed and easily 

 recognisable genus are at the present time known to occur in 

 the Ethiopian Region. The African species of Chrysops are of 

 medium size, not exceeding 10.5 mm. in length, and occasionally 

 considerably smaller. In the majority of cases the wings exhibit 

 a conspicuous black or dark brown band, running obliquely across 

 the surface from the more or less infuscated costal border (Plate II., 

 figs. 9-12, and Plate III., fig. 17) ; in Chrysops bicolor, Cordier 

 (C. nigriflava, Austen, Plate II., fig. 14) the distal margin of the 

 transverse band is less sharply defined, while in C. calida, Walk. 

 (Plate II., fig. 16), the band is wanting ; in C. dimidiata, v. d. Wulp, 

 and O. silacea, Austen (Plate II., figs. 13 and 14), rather more than 

 the distal half of the wings is infuscated. In the resting position 

 the wings are carried half open, that is with their tips more divergent 

 than in the case of Tabanus. The presence of three ocelli on the 

 crown of the head is characteristic of the genus, and the face and 

 front exhibit shining tubercles or calli ; occasionally the first joint 

 of the long antennae is conspicuously swollen (Plate II., figs. 14 



* BuUetindu Museum National d' Histoire Naturelle, Ann^e 1908, p. 283 (Paris, 1908). 



