SIMULIIDAE OF AFRICA 71 



arrangement of the gill. One species of this complex, S.(P.) impukane de Meillon, 

 however appears to differ from others so far known by having the posterior corners 

 of the male ventral plate prominent and by the presence of a strongly bent medio- 

 apical lip to the plate (figured by Freeman & de Meillon, 1953 : 73). The plate of 

 impukane could be described as having ' shoulders ' but the sides of the plate are 

 not pinched-in or excavated as in the cervicornutum-group or the kenyae-group. 



Most species of the alcocki-group, like those of the schoutedeni-group and the 

 cervicornutum-group, have rather pale legs in which the femora and tibiae are dark 

 at the apices and the hind tibiae have in addition a sub-basal dark band (well shown 

 in the figures of Freeman & de Meillon, 1953) ; it should be noticed, however, that in 

 S.(P.) merops and S.(P.) evillense the legs are rather uniformly dark brown and that 

 in this respect (as well as in the vestiture of the female abdomen mentioned above) 

 these two species are atypical for Pomeroyellum. 



An unusual pupal gill form occurs in S.(P.) schwetzi Wanson (Text-fig. 186) where 

 the seven main filaments are swollen along their length into a sausage-form, the 

 swollen parts having one or a pair of short terminal thread-like filaments to make up 

 ten filaments in all. The species is only known from the pupa, but since the gill 

 appears to be a modification from the 10-filament form found in the gill of many 

 alcocki-group forms it is best placed in this group, pending confirmation of this 

 position from the other stages when they become known. 



Included taxa. Simulium (Pomeroyellum) alcocki Pomeroy ; S. (P.) allaeri 

 Wanson ; S.(P.) coalitum Pomeroy ; S.(P.) djallonense Roubaud & Grenier ; 

 S.(P.) duodecimum Gibbins ; S.(P.) evillense Fain, Hallot & Bafort ; S.(P.) garmsi 

 nom. n. (= occidentale Freeman & de Meillon, preoccupied) ; S.(P.) geigyi Garms 

 & Hausermann ; S.(P.) gilleti Fain & Hallot ; S.(P.) hissetteum Gibbins ; S.(P.) 

 impukane de Meillon ; S.(P.) ituriense Fain ; S.(P.) johannae Wanson ; S.(P.) 

 merops de Meillon ; S.(P.) rodhaini Fain ; S.(P.) schwetzi Wanson ; S.(P.) tena- 

 culum Gibbins ; S.(P.) weyeri Garms & Hausermann. 



In addition the nomenclaturally unavailable form name sextumdecimum has been 

 applied by Luna de Carvalho (1962) to a taxon of this group. 



schoutedeni- group. <J hind basitarsus normal, slender ; styles normal ; ventral plate 

 excavate laterally near base of basal arms or with a lateral notch each side in ventral view, 

 shoulders well developed, rather thickened in profile. Pupal gill of filamentous type, eight 

 filaments arising from long common stem. Cocoon without neck. Larval abdomen with sparse 

 very large erect flattened scale-like setae, mainly dark and conspicuous, and with accessory 

 sclerites. Larval postgenal cleft large and much longer than postgenal bridge, broadly and 

 bluntly sagittate in shape. 



This small group, containing only two species at present, is completely intermediate 

 between the alcocki-group and the cervicornutum-group, showing a filamentous type 

 of pupal gill like the former but a larval stage with large flat abdominal scales, 

 accessory sclerites, and postgenal cleft like the latter group. On the basis of the 

 larvae the two species — if no other stages were known — would be immediately placed 

 in cervicornutum-group, whereas if the larvae were unknown they would fit the 

 alcocki-group on pupal characters ; if the two species were placed in either of these 



