SIMULIIDAE OF AFRICA 45 



pale and weakly sclerotized). Hypostomium with usual nine apical teeth, median and corner 

 teeth strongly prominent (Text-fig. 274) ; only 2-4 setae in each hypostomial row, rows lying 

 parallel to lateral margins of hypostomium, serrations prominent. Head pale, largely unpig- 

 mented, sometimes a little pigmentation on cephalic apotome but pattern neither clearly positive 

 or negative (sometimes areas where spots normally present rather paler than surroundings). 

 Postgenal cleft very large and reaching or almost reaching hypostomium, postgenal bridge 

 therefore incomplete or forming only narrow strip between apex of cleft and base of hypo- 

 stomium, if bridge incomplete then cleft widely reaching hypostomium. Mandible normal, 

 middle comb-tooth usually weaker than first or third, sometimes subequal to third; inner 

 mandibular margin rather convex, one serration with or without trace of a small blunt second 

 serration. Antenna of medium length, unpigmented, with four segments (except occasionally 

 first suture apparently obliterated). Thoracic and abdominal cuticle dorsally covered with 

 minute erect fan-shaped or scale-like setae. Abdomen with dorsolateral prominences, slightly 

 subconical, on first five or six segments, or if not at least with the mid ventral part of each of the 

 first few segments unusually prominent (segmentation of the narrow anterior part of abdomen 

 therefore always well marked). Ventral papillae small and subconical or virtually absent. 

 Accessory sclerites absent (or rarely slight trace). Rectal scales present. Rectal gills with 

 numerous secondary lobules. Posterior circlet with about 60-65 rows of 0-15 hooks. 



Bionomy. [Oviposition sites apparently unrecorded, eggs probably laid broad- 

 cast on water.] Larval and pupal stages non-phoretic ; attached to submerged 

 sticks, grasses, sedge, corn-stalks, fish-traps and other substrates in smooth or slightly 

 broken but moderately swift waters of large or very large rivers. Female ornitho- 

 philic or sometimes mammalophilic (including anthropophilic when occurring in 

 large outbreaks). 



Distribution. Scattered distribution throughout the mainland of the North 

 American, Eurasian and African continents. African distribution as in Map 11. 



Discussion. Byssodon is the only subgenus of Simulium s.l. in the Ethiopian 

 Region that has the basal section of the radius bare, and on account of this and 

 several other of its characters it is markedly isolated from all the endemic Ethiopian 

 subgenera : it is also the only subgenus (except for the cosmopolitan Ett simulium) 

 which is common to the Palaearctic and Ethiopian Regions. Rubzov (1959-1964), 

 in his monograph of Palaearctic Simuliidae, used the name Titanopteryx Enderlein 

 for the segregate, but Stone (1963) showed that the name Byssodon Enderlein applies 

 to the same concept and therefore that Titanopteryx falls as a synonym. This is 

 unquestionably correct, and in fact the type-species of Byssodon (Simulium meridi- 

 onale Riley) and of Titanopteryx (Simulium macidatum (Meigen)) — although the one 

 is from North America and the other from western Europe— have such identical 

 characters that they might even by synonymous. Baranov's genus-group name 

 Echinosimulium is also, as Stone (1963) noted, a synonym of Byssodon since (through 

 the synonymy of its type-species with macidatum Meigen) it is an isogenotypic 

 synonym of Titanopteryx. 



The synonymy of Psilocnetha with Byssodon, which is here newly established, is 

 not so clear-cut, but as the result of studies on the segregates of Simulium s.l. on a 

 world basis it has become apparent that the distinctions between the Ethiopian 

 Psilocnetha and Holarctic Byssodon are inadequate to justify the separation of the 

 two segregates as subgenera (although they are recognized here as separate species 



