62 R. W. CROSSKEY 



group, the only other group represented in the Ethiopian Region, by the one long 

 hook on each paramere of the male hypopygium (this is sometimes associated with 

 one or a pair of minute supernumerary hooks at the base), by the well defined keel 

 on the ventral plate and by the small or indefinitely developed postgenal cleft of the 

 larva. 



The ruficorne-group has successfully colonized several of the remote islands of the 

 Atlantic (St. Helena) and Indian oceans (Seychelles, La Reunion, Mauritius, 

 Rodriguez) , but it is not certain how the necessary transoceanic dispersal occurred — 

 in the case of St. Helena over at least 1200 miles from the nearest continental main- 

 land. Carriage on birds, since the ruficorne-group forms like other Eusimulium are 

 ornithophilic and in the female have large claw-teeth, is a possible explanation but 

 no evidence exists that Simuliidae can survive on birds for more than a very short 

 time. 



S.(E.) specidiventre, the only Simuliid occurring in the Seychelles Islands, differs 

 from typical ruficorne-group forms, however, by having the tooth on the claws of 

 the female very reduced, the male ventral plate rather narrow and with more 

 rounded posterolateral corners than usual, the suture apparently obliterated between 

 the first two segments of the larval antennae, and by having an exceptionally high 

 number of hooks in the posterior larval circlet (about 140 rows of 16-19 hooks) ; 

 despite these atypical features it appears best to assign specidiventre to the ruficorne- 

 group in preference to creating a special group for an exceptional species alone. 

 Freeman & de Meillon (1953 : 64) placed the species in their alcocki-group of 

 Simulium (now in the subgenus Pomeroyellurn) but this was before the discovery of 

 the immature stages ; these, recently described by Crosskey (1966), clearly show 

 that 5. specidiventre Enderlein belongs in the subgenus Eusimulium and not to 

 Pomeroyellurn. 



A second aberrant species here assigned to the n^com^-group on its balance of 

 characters is S.(E.) starmuhlneri from Madagascar (Grenier & Grjebine, 1963). The 

 characters of the male hypopygium including large broad ventral plate with median 

 keel, long narrow parameres with single large tooth, and shape of the style, conform 

 exactly to those of ruficorne-group, but the female has almost no trace of a claw-tooth, 

 the four exceptionally fine thread-like filaments of the pupal gill arise from a single 

 large elongate trunk (Text-fig. 180), the larval abdomen shows well developed traces 

 of a sclerotized accessory ring in front of the posterior circlet, and the larval mandible 

 has three mandibular serrations in place of the normal two ; though the species is 

 distinctive and atypical in the larval and pupal stages, the male hypopygial 

 characters confirm that the affinities of starmuhlneri are with other members of the 

 ruficorne-group. 



Enderlein's generic names Nevermannia, Stilboplax and Chelocnetha are all based 

 on species in the ruficorne-group (see synonymy of Eusimulium given above) and 

 are here treated therefore as synonyms of Eusimulium Roubaud ; they have not 

 been in use as genus-group names in the Simuliidae for the past quarter-century, 

 except by Japanese workers on the simuliid fauna of Japan and Ryukyu Is. who 

 have used the names Nevermannia and Stilboplax for subgeneric segregates (Ogata, 



