SIMULIIDAE OF AFRICA 41 



9 Gill formed of six or nine large thin-walled tubular filaments arising between a pair 

 of large inflated basal arms (Text-figs. 209, 210), all branches pale and of essenti- 

 ally the same kind EDWARDSELLUM Enderlein (p. 101) 



- Gill with filaments not of this type (except in cavum and natalense) .... 10 



10 Gill with one type of slender filament and without basal arms, filaments numbering 



6-19 (Text-figs. 200-202). [Malagasy Region only] XENOSIMULIUM sgen. n. (p. 86) 



- Gill with stout primary filaments and thinner secondary filaments or with enlarged 



tubular branches, often with basal arms (Text-figs. 21 1-2 16), if filaments all 

 slender except at the base (Text-fig. 214) then numbering at least 24. [Ethiopian 

 Region only] METOMPHALUS Enderlein (p. 96) 



11 Gill with four filaments (Text-figs. 174, 175, 177-180) (except in loutetense with six 



filaments as Text-fig. 176 and cocoon with neck) EUSIM ULIUM Roubaud (p. 56) 



- Gill not with four filaments (only with six filaments in sexiens but then cocoon simple) 12 



12 Gill filamentous, with 6, 8 or 11 filaments (Text-figs. 193, 194) 



MEILLONIELLUM Rubzov (p. 74) 



- Gill of very varied form (Text-figs. 181-192, 196) but never with 6 or 1 1 filaments and 



if with 8 filaments these not arranged as in Text-fig. 193 



POMEROYELLUM Rubzov (p. 66) 



13 Gill of filamentous type with 4, 6 or 8 filaments. At least one of the abdominal seg- 



ments 6-9 with dorsal spine-combs . . . . . . . . 14 



- Gill with a pair of large inflated thin-walled basal arms bearing thin-walled variously 



modified tubes between them (often with form similar to Text-fig. 207). Ab- 

 dominal segments 6-9 bare dorsally, all without trace of spine-combs 



W1LHELMIA Enderlein (p. 94) 



14 Gill with four filaments EUSIMULIUM Roubaud (p. 56) 



- Gill with more than four filaments . . . . . . . . . 15 



15 Gill with eight filaments arising in regular pairs (Text-fig^ 220). Cocoon simple, 



slipper-shaped without neck .... ODAGMIA Enderlein (p. 107) 



- Gill with six filaments. Cocoon with loosely woven neck showing large open 



fenestrations (Text-fig. 218) ......... 16 



16 Gill as in Text-fig. 217. Dorsum of eighth abdominal segment with spine-comb 



TETISIMULIUM Rubzov (p. 104) 



- Gill as in Text-fig. 219. Dorsum of ninth abdominal segment with spine-comb 



SIMULIUM Latreille s. str. (p. no) 



Larvae 



[Note: the key applies only to older and mature larvae and cannot be used for the early 

 instars, which for almost all forms are either unknown or have not been studied in detail] 



1 Forms from Ethiopian and Malagasy Regions ....... 2 



- Forms from North Africa and Canary Islands ....... 14 



2 Larvae attached to crabs. Hypostomium with rather even row of 13 apical teeth 



(Text-fig. 268). Mandible tapering-elongate and very little arched on outer edge 

 (Text-fig. 292). Body form as Text-fig. 284. Head elongate and cephalic 

 apotome rounded posteriorly (Text-fig. 283) . LEWISELLUM sgen. n. (p. 76) 



- Larvae not attached to crabs. Hypostomium, mandible, body form and shape of 



cephalic apotome not so ......... . 3 



3 Larvae attached to mayfly nymphs*. Posterior circlet in a subventral position 



(Text-fig. 285). Cephalic fans when open sometimes forming short flat brushes 

 (Text-fig. 286). Hypostomium sometimes of form shown in Text-fig. 267 



PHORETOMYIA sgen. n. (p. 79) 



- Larvae not attached to mayfly nymphs. Posterior circlet in the normal terminal 



position. Cephalic fans when open always forming normally shaped curved 

 brushes. Hypostomium never of this form ....... 4 



* or to river prawns, see Appendix. 



