58 R. W. CROSSKEY 



section under the latter name, and those between Eusimulium and Oriento-Austral- 

 asian subgenera Gomphostilbia and Morops have been discussed elsewhere (Crosskey, 

 1967a). Eusimulium differs from the New World segregate Psilopelmia by having 

 the cibarium of the female fully or almost unarmed, by having (with few exceptions) 

 a very large basal tooth to the claws of the female, usually by having only one very 

 strong parameral tooth with one or two minute additional teeth, and by having 

 positive larval head-spots : in addition the basal section of the radius is often bare 

 in Psilopelmia, whereas it is always haired in Eusimulium. 



In the African area Eusimulium covers a greater geographical range than any 

 other genus or subgenus of Simuliidae, despite the relative deficiency in the number 

 of species occurring in the Ethiopian and Malagasy Regions (Map 2) ; it occurs not 

 only in tropical and southern Africa, but also from Morocco to Tunisia, in Sinai 

 peninsula of Egypt, in South Yemen, Seychelles, Madagascar and the Mascarene 

 islands, and in St. Helena. It is not yet known from Libya, from which no 

 Simuliidae have been recorded, but probably occurs there. The subgenus contains 

 the only species of Simuliidae known from the Sahara : Simulium {Eusimulium) 

 ruficorne Macquart is a species adapted to survival in conditions of very reduced 

 flow, or even no flow at all, and has been recorded from the Tibesti and Tassili des 

 Ajjer massifs in the central Sahara. 



In the Palaearctic Region the Eusimulium fauna has been subjected to excessive 

 taxonomic splitting by some workers, usually on the basis of very slender morpho- 

 logical evidence provided by small differences in the male genitalia, and Rubzov 

 (1959-1964) recognizes a little over one hundred species from this region ; by 

 contrast, Stone (1965) lists only twenty species from America north of Mexico (but 

 states that aureum and latipes in this area are unrevised species complexes) . Despite 

 this great difference in the number of named entities in the Nearctic and Palaearctic 

 areas the Eusimulium fauna is essentially very similar, and most of the North 

 American species clearly fall into one or other of the seven species-groups of 

 Eusimulium delimited by Rubzov for the Palaearctic Region. Three of these 

 species-groups are clearly present in the fauna of Africa and its islands. 



The most primitive forms of Eusimulium, or at least those showing the greatest 

 number of characters resembling Prosimuliine black-flies, are those which lack a 

 definite pedisulcus and have a widely spaced series of serrations on the larval man- 

 dible. These form the annulum-group of Rubzov (1959-1964), otherwise called the 

 subexcisum-group by Davies (1966), and are not represented in the African fauna (in 

 which all species of Eusimulium have the pedisulcus well developed). An unusual 

 character in the annulum-group, not to be regarded as primitive, is the presence of 

 secondary annulations on the larval antenna : this feature does not occur in the 

 larvae of any African species. 



In the North American fauna five species, S.(E.) anatinum Wood, S.(E.) con- 

 gareenarum (Dyar and Shannon), S.(E.) excisum Davies, Peterson & Wood, S.(E.) 

 innocens (Shewell) and S.(E.) rivuli Twinn, form a natural group in which the 

 pedisulcus is very shallow, the male style long and tapering, there are many para- 

 meral teeth, the larval antenna is most often secondarily annulated, and in which 



