276 MEDICAL ENTOMOLOGY 



admedian dark bands ; abdomen of a steely grey. According to Neave 

 it is widely distributed in the wooded parts of eastern tropical Africa. 



Hine gives the following Key to the North American genera of 

 Tabanidae : 



1. Hind tibiae with spurs at the tip ......... 2 



Hind tibiae without spurs .......... 6 



2. Third segment of the antenna composed of eight annuli the first 



of which is only a little longer than the following ones .... 3 



Third segment of the antenna composed of only five annuli 

 the first of which is much longer than the following ones ; 

 ocelli present ............ 5 



3. Front of male narrow ; ocelli present or absent ; fourth pos- 



terior cell at least open ....... Pangonia. 



(Diatomineura, Corizoneura.) 

 Front of female broad with a denuded callus ; ocelli present .... 4 



4. Eyes in the female acutely angulated above ; wing in both 



sexes with a dark picture ....... Goniops. 



Eyes in the female not acutely angulated above ; wings 



hyaline '. Apatolestes. 



5. Second segment of the antenna about half as long as the first ; 



eyes in life with numerous small dots ..... Silvius. 

 Second segment of the antenna as long or but little shorter 



than the first ; wing with a dark picture .... Chrysops. 



6. Third segment of the antenna with a well developed basal 



process Tabanus. 



(Therioplectes. Atylotus.) 

 Third segment of the antenna without, or with a rudimentary 



basal process ............ 7 



7. All the tibiae enlarged, the hind pair ciliate .... Snowiellus. 

 None of the tibiae enlarged and the hind pair not ciliate. .... 8 



8. Front of the female as broad as long ; the callus transverse . Hematopota. 

 Front of the female narrow Diachlorus. 



GENUS TABANUS, L. 



Small to very large thick-set insects. The head is as a rule broader 

 than it is high; the eyes may be nude or hairy. In the male the eyes 

 have irridescent bands, in which the facets are larger than in the rest of 

 the surface. The colours of these bands fade rapidly on the death of the 

 insect. In the female there are no irridescent bands and the colouration 

 is usually uniform ; in some species the females have brightly coloured 

 bands, in which case the eyes of the male are similarly marked on the 

 lower surface. In a few species (subgenus Therioplectes, Zeller) the eyes 

 are pubescent, but the hairs as a rule are not very apparent. Ocelli are 

 always absent, but there may be a small tubercle on the vertex (Therio- 

 plectes) ; it is absent in the subgenus Atylotus. The eyes of the female 

 are widely separated; situated on the forehead between them there are 



