SIMULIIDAE OF AFRICA 67 



of varied form, subtriangular or a broad transverse plate, with or without well developed 

 shoulders, basal arms short and directed forwards ; median sclerite simple rod-like, sometimes 

 dilated apically ; parameres long and slender, each with one very long scythe-shaped parameral 

 hook and usually one or two much smaller hooks arising from base of main one. Pupa : Gill of 

 very varied forms, filamentous or with antler-like or sausage-like branches variously modified, 

 when filamentous not less than seven filaments in each gill ; gill as long as or shorter than body 

 of pupa. Abdominal onchotaxy normal, sometimes one or a pair of minute supernumerary 

 hooklets each side ventrally on segment 4 and sometimes row of minute hooklets each side dors- 

 ally on segment 2 ; abdominal segments 7 and 8 (sometimes also 6 or 9) dorsally with spine- 

 combs. Cocoon without neck (except in kenyae), sometimes with short median dorsal projection. 

 Larva : Head and cephalic fans normal. Hypostomium with usual nine apical teeth, these 

 usually sharp-pointed and median and corner teeth prominent ; hypostomial setae 3-5 in each 

 row, rows lying parallel to lateral margin of hypostomium. Head-spots negative, on cephalic 

 apotome usually surrounded by dark pigmentation forming H-shaped mark (Text-figs. 232- 

 234). Postgenal cleft of medium size or large, equal in length to or much longer than postgenal 

 bridge, rounded, helmet-shaped or mitre-shaped. Mandible normal, second comb-tooth smaller 

 than first or third ; two mandibular serrations without supernumeraries. Antenna long and 

 slender, with four segments. Thoracic cuticle bare or with minute colourless setae. Abdominal 

 cuticle posterodorsally with small divided fan-like setae or large spatulate setae, bare in a few 

 forms. Abdominal shape normal, broadest in profile at sixth or seventh segment. Ventral 

 papillae present. Accessory sclerites present or absent. Rectal scales present. Rectal gills 

 usually with secondary lobules, sometimes one or all lobes simple. Posterior circlet with 60-85 

 rows of 8-16 hooks. 



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

 phoretic ; attached mainly to dead leaves and trailing roots and grasses in slowly- 

 flowing waters of small streams, occasionally in rapids of larger rivers or in swift 

 cascades. Female ornithophilic. 



Distribution. Widespread throughout the Ethiopian Region, excluding southern 

 Arabia (Map 3), and occurring also in Madagascar. 



Discussion. Pomeroyellum is the largest endemic Ethiopian subgenus, containing 

 about thirty per cent of the species and forms of Simidium s.l. from the region. The 

 segregate appears to be rather closely allied to Eusimulium ; in fact it is difficult to 

 separate the males of Eusimulium and Pomeroyellum by a completely satisfactory 

 diagnosis, and the females of those forms of Pomeroyellum in which the abdomen is 

 evenly covered with pale scales are indistinguishable subgenerically from Eusimu- 

 lium. The two subgenera are most clearly separated on characters of the larva : 

 the larvae of Pomeroyellum have a negative head pattern of pale spots surrounded or 

 separated by dark infuscation (Text-figs. 232-234), and the dorsal abdominal cuticle 

 is almost always armed with divided fan-like or large scale-like setae (Text-figs. 

 224 & 225) ; in Eusimulium the larval head-spots are always positive (Text-figs. 235 

 & 236), and the abdominal cuticle is almost always bare but occasionally has minute 

 simple colourless hairs. In the pupal stage of Pomeroyellum the gill, if of the fila- 

 mentous type, never has less than seven filaments, whereas four or six filaments are 

 found in Ethiopian forms of Eusimulium (though eight or more occur in some 

 Holarctic Eusimulium) and the cocoon in Pomeroyellum never has a very long horn- 

 like median process like that of many Eusimulium species. The range of pupal gill 

 form in Pomeroyellum includes non-filamentous shapes (Text-figs. 187-192) such as 



