SIMULIIDAE OF AFRICA 91 



fore tarsi slender, numerous parameral hooks, haired ventral plate, frons of female 

 pollinose, female abdomen with more or less even scale covering, pupal gill filamen- 

 tous but filaments usually rather stiff, pupal abdomen without dorsal spine-combs on 

 terminal segments, cocoon with well formed neck, larval head with positive head- 

 spots and hypostomial setae divergent posteriorly from margins of hypostomium, 

 larval cuticle bare or at most with sparse minute setae posterodorsally, similar 

 larval abdominal shape and no ventral papillae. The differences from Freemanellum 

 and Xenosimulium are indicated in the discussion sections for these subgenera (q.v.). 



The subgenus Anasolen, which is so strikingly orophilic, perhaps originated in 

 eastern Africa in the mountain-building Pliocene period, thence possibly dispersing 

 from an original East African locus into southern and West Africa and through 

 Ethiopia via the Pliocene land-bridge into southern Arabia (where the type-species, 

 5. dentidosum, is known to occur : see Crosskey, 19676 : 5). At least such hypo- 

 thesis would account for the known pattern of distribution for the subgenus (Map 7). 

 On the other hand, the existence of A nasolen-\\ke forms in South America (i.e. 

 subgenus Grenierella) might, assuming that the resemblance is due to recent mono- 

 phyly and not to convergence through occupation of a similar ecological niche, imply 

 quite another origin for the group. 



Some forms of Anasolen that occur on Mt. Kenya and on Ruwenzori from about 

 10,000 feet above sea-level to the highest glacier-melt streams at about 13,000- 

 14,500 feet (the very highest altitudes at which Simuliidae occur in Africa) are 

 remarkable for structural modifications to the female head and mouthparts that 

 occur in no other Ethiopian Simidium : McCrae (personal communication) has 

 found that the females are microcephalic and that the mouthparts lack well developed 

 apical teeth for biting, the latter feature suggesting that they cannot bite and are 

 presumably therefore autogenous. The head of the microcephalic forms, both 

 anteriorly and posteriorly (for instance in shape of the occipital foramen, postgenal 

 lobes and extent of the postgenal membrane), does not differ noticeably from that of 

 normal forms except in its reduced size. 



The pupal gill in Anasolen species shows all numbers of filaments from 8 to 19, 

 except for 13 — which number of gill-filaments has not been found in any pupa 

 despite the occasional variability that sometimes occurs (McCrae, personal com- 

 munication). 



There is a close uniformity in the species of Anasolen and no separate species- 

 groups are recognized within the subgenus. 



Included taxa. Simidium (Anasolen) bisnovem Gibbins ; 5.(^4.) dentidosum 

 Roubaud ; S.(A.) kauntzeum Gibbins ; 5.(^4.) masabae Gibbins ; S.(A.) ngabogei 

 Fain ; S. (A. ) nili Gibbins ; S. (A. ) octospicae Gibbins ; S. (A. ) rhodesiense de Meillon; 

 S.[A.) shoae Grenier & Ovazza ; S.(A.) voltae Grenier, Ovazza & Valade. 



[Note : Simulium (Anasolen) nili Gibbins was only known with certainty from 

 the type-locality of the Victoria Nile near Jinja, Uganda, and appears to have been 

 incidentally eradicated by insecticidal control operations on the Victoria Nile 

 directed against Simulium (Edwardsellum) damnosum Theobald.] 



