SIMULIIDAE OF AFRICA 69 



It is probable that Pomeroyelhim and Psilopelmia evolved independently from 

 Eusimulium-like forms ; the latter subgenus may be looked upon as the equivalent 

 group in the Neotropical Region to Pomeroyelhim in tropical Africa. Both sub- 

 genera form predominant elements in their respective faunae and tend to occupy the 

 warmer lowland streams. In Africa, Pomeroyelhim is the main slow-water com- 

 ponent of the black-fly fauna and forms the counterpart in slow streams to the main 

 endemic Ethiopian subgenus Metomphalus found in the swift broken or cascading 

 streams. 



The species of Pomeroyelhim fall into several distinct groups, principally on 

 characters of the immature stages. The groups here recognized are keyed and 

 defined below. 



Key to the Species-Groups of the Subgenus POMEROY ELLU M 



1 Hind basitarsus of <J greatly dilated, only about 28 times as long as its greatest 



breadth. Cocoon with neck. Pupal gill with eight filaments arising near base in 

 regular pairs (Text-fig. 184). Larval postgenal cleft with flattened-cordate shape 

 (Text-fig. 249) kenyae-£roup (p. 73) 



- Hind basitarsus of $ normal, not dilated and about six times as long as its greatest 



breadth. Cocoon without neck. Pupal gill and larval postgenal cleft of different 



form .............. 2 



2 Larval cuticle bare. Pupal gill formed of a single long forwardly directed tube 



divided apically into eight small thread-like filaments (Text-fig. 181) or with a single 

 long recurved wrinkled tube (Freeman & de Meillon, 1953, fig. 23c). Style small 

 relative to coxite and wide at base (Text-fig. 141) . . bequaerti- group (p. 69) 



- Larval cuticle with divided setae or scales posterodorsally on abdomen. Pupal gill 



not of these forms. Style larger in relation to coxite and longer and narrower 

 (Text-fig. 140) 3 



3 Larval abdomen with large conspicuous erect scale-like setae (Text-figs. 224 & 



225(a) ) and with accessory sclerite on each side of last segment. Larval post- 

 genal cleft large and mitre-shaped (Text-fig. 248) or bluntly sagittate, much longer 

 than postgenal bridge. <J ventral plate pinched-in or at least slightly constricted 

 laterally and with posterolateral 'shoulders' (Text-fig. 99). Pupal gill usually not 

 filamentous, if so then eight filaments arising from long common stalk ... 4 



- Larval abdomen with small inconspicuous semi-recumbent divided setae, usually fan- 



shaped (Text-fig. 2 25(b, c) ) and without accessory sclerites. Postgenal cleft 

 smaller and rounded or helmet-shaped (Text-figs. 246 & 247), subequal in length to or 

 shorter than postgenal bridge, <J ventral plate of varied shape but not excavate 

 laterally and therefore without posterolateral 'shoulders' (Text-figs. 96-98). 

 Pupal gill filamentous and with 7-20 filaments, sometimes arising from common 

 stem or trunk, if eight then not on common stem . . alcocki- group (p. 70) 



4 Pupal gill filamentous, eight filaments arising from long common stem (Text-fig. 185) 



schoutedeni-Qroup (p. 71) 



- Pupal gill not filamentous, of varied form (Text-figs. 187-192) cervicornutum-&roup (p. 72) 



bequaerti- group, o* hind basitarsus normal, slender ; style short and broad at base, small 

 in relation to coxite ; ventral plate not noticeably excavate laterally, without definite shoulders, 

 slender in profile. Pupal gill with one long slender undivided filament or with a very long fila- 

 ment branched into eight at apex. Cocoon without neck. Larval cuticle bare, abdomen with- 

 out accessory sclerites. Larval postgenal cleft subquadrate or helmet-shaped (Text-fig. 247), 

 subequal in length to postgenal bridge. 



