102 R. W. CROSSKEY 



style with one apical spinule ; coxite at least slightly produced beyond base of style ; ventral 

 plate complex, basal arms divergent, strongly arched in profile, body of plate more or less 

 toothed ; median sclerite with biramous apex at right angles to body of sclerite or straight and 

 cleft apically, not toothed ; parameres narrow, parameral hooks numerous. Pupa : Gill formed 

 of large thin-walled tubes comprised of a pair of basal arms and six or nine filaments arising be- 

 tween these. Abdomen with normal onchotaxy ; segments 6-9 without spine-combs dorsally. 

 Cocoon with well formed neck, shoe-shaped. Larva : Head and cephalic fans normal. Hypo- 

 stomium with usual nine apical teeth, these short and blunt (Text-fig. 282) ; 4-6 setae in each 

 hypostomial row, rows divergent behind from lateral margins of hypostomium. Head-spots 

 positive, head often heavily pigmented. Postgenal cleft very large, rounded-cordate or almost 

 circular, occupying most of venter of head, postgenal bridge very reduced in mid-line so that cleft 

 may nearly reach base of hypostomium. Mandible normal, first three comb-teeth subequal, two 

 serrations (smaller one sometimes missing). Antenna short, with four segments. Thoracic 

 cuticle (including that of proleg) and abdominal cuticle extensively covered with flattened lance- 

 olate or ovate scales. Abdomen with paired dorsolateral swellings or subconical prominences on 

 first five segments (Text-fig. 230), these especially conspicuous even when small through aggrega- 

 tion of dark scales. Ventral papillae absent. Accessory sclerites absent or represented by small 

 sclerotized platelets. Rectal scales present or (apparently) sometimes absent. Rectal gills 

 compound, each lobe with numerous slender finger-like secondary lobules. Posterior circlet 

 with 120-170 rows of 18-45 hooks. 



Bionomy. Eggs clustered, adhered to substrate. Larval and pupal stages non- 

 phoretic ; most often attached to trailing vegetation in rapids of moderate to large 

 size rivers, less commonly in streams or on stones and rock surfaces. Attachment of 

 eggs, larvae and pupae very characteristically occurs on grasses dipping into fast 

 broken water. Female mammalophilic, including anthropophilic ; also ornitho- 

 philic. 



Distribution. Widespread in the Ethiopian Region (Map 10), excluding southern 

 Arabia. The range extends further northwards along the Nile valley than in other 

 subgenera (except Byssodon) and reaches as far as the Second Cataract of the Nile 

 near the Egyptian border with Sudan ; it includes also the island of Fernando Po 

 in the Gulf of Guinea. The subgenus is absent from the Malagasy Region. 



Discussion. Edwardsellum is the most easily recognized subgenus of Simulium in 

 the Ethiopian Region because of the distinctive larvae, with their striking covering 

 of scales and paired swellings or tubercles on the first five segments of the abdomen 

 (Text-fig. 230), and because of the enlarged fore tarsi of the adults (Text-fig. 82). 

 No similar larvae occur in the Ethiopian fauna, and the only other Ethiopian sub- 

 genus with dilated fore tarsi is Phoretomyia ; males of Edwardsellum can easily be 

 distinguished, however, from those of Phoretomyia by the bold black and silver-grey 

 pattern on the scutum (usually much as in Text-fig. 77) and both sexes are very 

 different in the terminalia. There is certainly no relationship between these sub- 

 genera, and a dilated fore tarsus is clearly a character derived independently in the 

 two groups. 



The subgenus Edwardsellum has no affinity with, or no close resemblance to, any 

 New World subgenus or to any of the subgenera occurring in the Oriento-Austral- 

 asian Regions. There is a superficial similarity between the males of Edwardsellum 

 and those of some Oriental species of Simulium s.l. placed by Edwards (1934) in his 



