36 R. W. CROSSKEY 



characters that never occur in the Simulium fauna of the Ethiopian Region. It 

 may therefore be helpful to workers in other regions, who may wish to make quick 

 comparisons of their local fauna with that of Africa, to enumerate some of the 

 characters that are common to all or almost all Simulium found in the Ethiopian 

 Region. These characters are found in all Simulium species throughout Ethiopian 

 Africa (except where otherwise indicated) : — 



Calcipala well developed. 



Cibarium of $ unarmed (except in S. vorax and immediate allies). 



Antenna with n segments. 



Prothoracic precoxal bridge complete. 



Basal section of radius haired (except Byssodon species). 



Style of (J hypopygium with one spinule (except in S. wellmanni). 



Non-faceted area present on eye adjacent to antennal excavation. 



Frons of $ never iridescent. 



Scutum of $ never with scale vestiture arranged in small clumps. 



Postgenal bridge of larva complete (even if reduced to very narrow strip 



medially behind hypostomium). 

 Last larval abdominal segment without annular sclerotization. 



Keys to the Subgenera of SIMULIUM in Africa and its Islands 



Note : in order not to complicate the keys unnecessarily the first segregation is by geographical 

 area since in practice it will be known whether material originates from Palaearctic Africa or 

 from the Ethiopian and Malagasy Regions ; Eusimulium is the only subgenus common to both 

 areas and this is run out twice. Likewise with the immature stages of Ethiopian forms it will 

 always be known whether they are phoretic forms associated with crabs or mayfly nymphs, and 

 for convenience they are segregated first in the Ethiopian section of the keys by their phoretic 

 habit : this avoids the difficulty of placing individual phoretic species that are aberrant in 

 certain larval or pupal features. Pupal characters given, especially of the gill or cocoon form, in 

 these keys for Africa will not necessarily hold for extra-limital forms of those subgenera occurring 

 also in other regions. The keys are artificial and juxtaposition of subgenera does not imply close 

 phyletic relationship. 



Males 



i Forms from Ethiopian and Malagasy Regions ....... 2 



- Forms from North Africa and Canary Islands . . . . . . . 14 



2 Basal section of radius bare. Hypopygium as in Text-fig. 95, ventral plate as in Text- 



figs. 107, 130 . . . . . BYSSODON Enderlein (p. 44) 



- Basal section of radius haired. Hypopygium not so ...... 3 



3 Katepisternum haired. Thoracic ground colour orange-brown to dark reddish 



brown. Styles long and slender, exceeding length of coxites (Text-figs. 91, 147). 

 Ventral plate as Text-figs. 110-112, 131 . FREEMANELLUM sgen. n. (p. 92) 



- Katepisternum bare. Thoracic ground colour almost always blackish. Styles at 



most subequal in length to and usually shorter than coxites. Ventral plate not so 4 



4 Fore tarsi conspicuously enlarged and with dorsal hair-crest (Text-figs. 81, 82), 



basitarsus 3 -5-5 times as long as its greatest breadth (except in berneri) . . 5 



- Fore tarsi not strongly dilated and without thick hair-crest, basitarsus usually 5-5-8 



times as long as its greatest breadth (Text-figs. 78-80, 83) ..... 6 



