6 R. W. CROSSKEY 



(1953) because they are enumerated in the ' Included taxa ' section under each genus, 

 subgenus or species-group of Simulium as appropriate, and are listed in the summary 

 of the proposed classification. Freeman & de Meillon (op. cit.) when working out 

 the Ethiopian fauna were faced with the fact that almost identical or at least very 

 similar adults are often associated with pupae in which the form of the gills differs 

 conspicuously and rather constantly, and in order to express this in taxonomy 

 introduced the concept of the ' pupal form ' (though there had been some previous 

 use of the term ' variety ' for forms with slight gill differences) : all forms were 

 treated as conspecific if the adults were not distinguishable, and the single species 

 regarded as polymorphic in the pupal stage. Workers in other regions had usually 

 treated wide differences in pupal gill as evidence that different species were involved, 

 even if the larvae and adults were not readily distinguishable, as for instance with 

 Simulium (Wilhelmia) equinum (L.) and S.(W.) salopiense Edwards. There is still 

 no means of ' proving ' whether forms in the sense of Freeman & de Meillon (1953) 

 are pupal polymorphs within a species, or whether the differing pupae are those of 

 biologically distinct species, but since there are small consistent differences also in 

 associated larvae, and I suspect in adults if studied sufficiently, I think it preferable 

 to regard all the pupal forms tentatively as distinct species (at least until clear 

 evidence is forthcoming to show otherwise) : I therefore cite the names of all of 

 them in specific status wherever they occur in the paper, but have used the term 

 ' Included Taxa ' (in preference to the more usual ' included species ') to emphasize 

 the element of doubt about the status of some of the inclusions. 



The following points should be noted about the geographical and bionomic 

 information given : 



The distribution maps for the subgenera are based on known localities (shown by 

 circle or triangle symbols) for all included species derived from material seen and 

 published records ; the approximate limits of subgeneric distribution are shown by 

 a solid line. The maps show certain areas within the presumed range but for which 

 information is lacking : the main ones are indicated by question marks. For 

 Palaearctic subgenera that occur in Africa the distribution is only shown on the 

 maps for the Mediterranean area. 



Although some species are very catholic in their choice of breeding site or in 

 female host preference there is a clear tendency for the constituent species of any 

 subgenus to have similar ecological requirements for the early stages and a similar 

 female host choice, and therefore for one subgenus to differ characteristically in 

 behaviour from another. A brief summary of the main features of the bionomy has 

 been given for each subgenus found in the Ethiopian and Malagasy Regions, but it 

 must be appreciated that these are generalizations for the subgeneric taxon as a 

 whole to which exceptions may occur in individual species. 



The text-figures given illustrate the main characters found in the supraspecific 

 taxa recognized, and show the range of form occurring within a taxon when there is 

 considerable variability (as in the pupal gill) . Some figures, especially of the pupal 

 gill, have for convenience been redrawn from Freeman & de Meillon (1953) or from 

 the same slides as were used by these authors. 



