SIMULIIDAE OF AFRICA 37 



5 Scutum with sharply defined black and silver-grey pattern (as Text-fig. 77 or with 



the dark vittae confluent medially). Parameral hooks numerous. Ventral plate 

 strongly arched in profile, toothed, form complex (Text-figs. 118, 136, 137). 

 Style truncate and coxite produced beyond base of style at least slightly (Text-fig. 

 150) . . . . . . . EDWARDSELLUM Enderlein (p. 101) 



- Scutum without such pattern. One long strong parameral hook on each side, some- 



times rudimentary. Ventral plate lamellate, with small basal arms and not 

 arched in profile or toothed (Text-figs. 106, 128). Style subconical and coxite not 

 produced beyond its base (Text-fig. 146). [Pharate $ attached to mayfly nymphs] 



PHORETOMYIA sgen. n. (p. 79) 



6 Hypopygium with one long strong dagger-shaped or scythe-shaped parameral hook on 



each side (Text-figs. 88, 89), usually directed outwards and occasionally with one 

 or two supernumeraries at its base. Ventral plate lamellate or subtriangular 

 (Text-figs. 96-101), never toothed and rather straight in profile (Text-figs. 120- 

 127). Scutum without pattern (except in Dexomyia from St. Helena) ... 7 



- Hypopygium with multiple parameral hooks on each side, at least four or five and 



usually many (Text-figs. 90, 92). Ventral plate of complex and varied form 

 (Text-figs. 114-117), often toothed and usually strongly angulate in profile (Text- 

 figs. 132-135), sometimes lamellate. Scutum at least with trace of silvery grey 

 shoulder patches, sometimes with bold pattern . . . . . . 11 



7 Scutum patterned as in Text-fig. 310. Pleural membrane sparsely haired. [St. 



Helena Island only] ...... DEXOMYIA sgen. n. (p. 49) 



- Scutum without pattern. Pleural membrane bare (except in adersi) ... 8 



8 Style abruptly contracted before the apex, usually narrowed on about apical third 



(Text-fig. 145). Ventral plate longer than broad or subquadrate, with small bent 

 basal arms and median apical approximately U-shaped notch (Text-fig. 105). 

 The parameral hook very conspicuous and with supernumeraries at its base 

 (Text-fig. 89) 9 



- Style not abruptly narrowed on apical part (Text-figs. 140, 141, 143, 144). Ventral 



plate transverse or subtriangular in the body with longer basal arms (Text-figs. 

 96-101). Parameral hook often with one or two supernumeraries arising from 

 its extreme base ............ 10 



9 Small forms, wing-length 1 -9-2 -5 mm. Basal margin of ventral plate between basal 



arms slightly bilobate or produced medially MEILLONIELLUM Rubzov (p. 74) 



- Large forms, wing-length 2-6-3-6 (usually about 3-0) mm. Basal margin of ventral 



plate between basal arms more or less smoothly rounded. [Pharate $ attached to 

 crabs] LEWISELLUM sgen. n. (p. 76) 



10 Ventral plate strongly transverse, with median keel and shoulders well developed 



(Text-figs. 88, 101) EUSIMULIUM Roubaud (p. 56) 



- Ventral plate less strongly transverse, anterolateral shoulders sloped or plate sub- 



triangular (Text-figs. 96-98), if plate transverse then without strong median keel 

 (Text-fig. 99) POMEROYELLUM Rubzov (p. 66) 



1 1 Scutum with silver-grey pruinose shoulder marks or with a bold black and pale grey 



pattern (Text-fig. 76 or similar to Text-fig. 75). Ventral plate of diverse form 

 (Text-figs. 114-117, 133-135), most often subtriangular and toothed apically 

 (Text-fig. 92). Pleural membrane bare (except in letabum and natalense) 



METOMPHALUS Enderlein (p. 96) 



- Scutum without silvery grey shoulder marks or black and grey pattern. Ventral 



plate differently formed, never toothed. Pleural membrane bare or haired . . 12 



12 Ventral plate very broad rectangular (Text-fig. 103), usually with haired bent mid- 



apical lip. Pleural membrane bare loutetense-group EUSIMULIUM (p. 63) 



- Ventral plate narrower, less flat and rectangular. Pleural membrane usually 



haired ............. 13 



