70 R. W. CROSSKEY 



This small group differs from all other Pomeroyellum for which the larval stage is 

 known by having the larval cuticle entirely bare and thus resembling that in sub- 

 genus Eusimulium ; the head-spots, however, appear to be negative (although only 

 poorly preserved material has been seen) and the male, female and pupal characters 

 are also those of Pomeroyellum so that assignment to this subgenus is best. The 

 style of the male is unusual as it is notably shorter and broader basally than in other 

 species-groups and thus appears rather small when compared to the coxite. The 

 pupal gill of harrisoni (figured by Freeman & de Meillon, 1953 : 86), formed by a 

 single long wrinkled tube curved round to the opposite side of the pupal body and 

 back towards the abdomen, is very exceptional and I know of no similar gill in any 

 other species of Simuliidae. 



Included taxa. Simulium (Pomeroyellum) bequaerti Gibbins ; S.(P.) harrisoni 

 Freeman & de Meillon. 



alcocki- group. o* hind basitarsus normal, slender ; styles normal ; ventral plate not con- 

 stricted or noticeably excavate laterally, body of plate sometimes subtriangular without pro- 

 minent posterolateral shoulders, narrow and slightly curved in profile (Text-figs. 120 & 121). 

 Pupal gill of filamentous type with from 7-20 filaments variously arising (but not with 8 filaments 

 arising from end of common stem, cf. schoutedeni-group) . Cocoon without neck. Larval 

 abdomen with divided setae, bifid or compound and fan-like, small and usually more or less 

 recumbent ; accessory sclerites absent. Larval postgenal cleft of medium size, subequal in 

 length to postgenal bridge, subquadrate or rounded (usually much as in Text-fig. 246). 



The alcocki-group as here defined corresponds in the main with the group treated 

 under this name by Freeman & de Meillon (1953), but in a slightly more restricted 

 sense, since the bequaerti-group, schoutedeni-group and S.(P.) kenyae are here exclu- 

 ded. Freeman & de Meillon (op. cit. : 64) placed Simulium speculiventre Enderlein 

 from the Seychelles in their alcocki-group, but as shown elsewhere in this paper 

 speculiventre is actually a species of Eusimulium ; no species of subgenus Pomeroy- 

 ellum are known from any of the small islands of the Indian Ocean. The group 

 includes more species and forms of doubtful taxomonic status than the other species- 

 groups of Pomeroyellum, and many of the species are found rather sparsely as 

 immature stages, attached mainly to dead leaves in small slowly-moving streams 

 throughout lowland Africa. 



Most species in the female have the posterior part of the abdomen rather bare and 

 shining, as is typical for the whole subgenus, but in S.(P.) merops de Meillon and 

 S.(P.) evillense Fain, Hallot & Bafort the whole abdomen of the female is thickly 

 covered with silvery scales (recalling Eusimulium, in which most females show an 

 even abdominal covering vestiture) ; despite this feature, merops and evillense are 

 assigned to the alcocki-group on balance of characters from the male or pupa, but it 

 should be noted that the larvae of these two species are unfortunately still unknown 

 (and could show characters that conflict with the definition of the group given 

 above) . 



The taxa in the alcocki-group in which there is a 10-filamented gill form a difficult 

 complex taxonomically that probably contains several sibling or semi-sibling species 

 showing differences only in very minor detail of the male genitalia or exact branching 



