SIMULIIDAE OF AFRICA 87 



attached mainly to stones and rock surfaces in clear swift cascading streams. 

 Female mammalophilic, including anthropophilic. 



Distribution. Confined to the Malagasy Region, where widespread in Madagascar 

 (Map 7) and known also from Comoro Islands. 



Discussion. Grenier & Grjebine (1958 : 986), when describing Simulium ambosi- 

 trae from Madagascar, pointed out that ' Cette espece, comme 5. neireti Roubaud et 

 S. imerinae Roubaud, fait partie du groupe dentulosum (Division B, groupe VI, de 

 Freeman et de De Meillon) dans lequel les especes malgaches imerinae, iphias, 

 ambositrae paraissent constituer un sous-groupe homogene ' ; in the present work 

 it is considered that this homogeneous group, endemic in the Malagasy Region, is 

 best ranked as a separate subgenus near to, but distinct from, the subgenus Anasolen 

 (i.e. the dentulosum-gvoup in the restricted sense). The name Xenosimuliiim is here 

 proposed for the subgenus, and Simulium imerinae Roubaud (since it is the species 

 best known in all stages and both sexes) is designated as type-species. 



Xenosimuliiim sgen. n. is the only subgeneric segregate of Simulium s.l. that is 

 confined to the Malagasy Region, where it forms the main component of the Simuliid 

 fauna in Madagascar. It differs from all Simulium found in the Ethiopian Region 

 by the unusual form of the enlarged, pointed and inwardly-directed female gonapo- 

 physes (Text-fig. 161) and by the secondarily annulated larval antenna, which 

 appears to have seven or eight segments instead of the normal four (Text-fig. 290). 

 The larvae are also remarkable because of the very prominent and enlarged almost 

 semi-circular form of the primary brush of the mandible (Text-fig. 296) which makes 

 them almost unique among Simuliid larvae from the African area as a whole, 

 although a smaller but somewhat similar development of the primary brush occurs 

 in the larvae of 5. (Freemanellum) debegene de Meillon from the African mainland ; 

 the reduction of the apical teeth and relative enlargement of the comb-teeth of the 

 larval mandible is also a striking feature (Text-fig. 302). The larval rectal gills 

 consist of three simple undivided lobes, without the numerous finger-like secondary 

 lobules that are normally found in the larvae of cascade-inhabiting forms, and this 

 character among others already mentioned distinguishes larvae of Xenosimulhtm 

 from those of Freemanellum, Anasolen, and Metomphalus that have superficially 

 similar larvae with the same body shape and lack of ventral papillae. The pupal 

 thorax in Xenosimulium species is unusual in having small very sharp spinous 

 tubercles in place of the normal flattened disc or platelet-like tubercles that are 

 normally found on the thoracic dorsum in the majority of Simulium s.l. species. 



Xenosimulium has the most characters in common with Anasolen and Freeman- 

 ellum from the Ethiopian mainland, although there is a marked concordance of 

 characters with the Neotropical subgenus Grenierella Vargas & Diaz Najera. It is 

 most likely that Xenosimulium is closely related to Anasolen and Freemanellum, 

 especially the latter, and that the group derives from forms that reached Madagascar 

 from Africa : there is no evidence to suggest an Oriental origin, and Xenosimulium 

 shows no affinity with any segregate in the Oriento-Australasian Regions (or with 

 the Holarctic fauna). 



Aside from the female genital, larval antennal and mandibular, and larval rectal 



