ioo R. W. CROSSKEY 



The scutum of the male in this group varies from mainly velvety black with some 

 silvery scaling laterally and posteriorly, and with silvery triangles anteriorly, to a 

 very well defined black and silver pattern in which three separated black vittae 

 occur : the latter form is particularly well developed in S. chutteri (Text-fig. 76) and 

 resembles the pattern found in males of Edwardsellum (Text-fig. 77). 



Included taxa. Simulium (Metomphalus) arnoldi Gibbins ; S.(M.) bovis de 

 Meillon ; S.(M.) chutteri Lewis ; S.(M.) fragai Marini de Araujo Abreu ; S.(M.) 

 janzi Marini de Araujo Abreu ; S.{M.) wellmanni Roubaud. 



medusaeforme- group. Medium-sized to large species, wing length 2-4-3-6 mm. $ 

 scutum without very definite pattern, only with pair of anterior silvery triangles (often in- 

 distinct) in addition to pale-scaled margins, o* ventral plate toothed apically, with widely 

 divergent basal arms ; coxite not produced beyond base of style. $ cibarium unarmed or 

 weakly toothed between cornuae. Pupal gill with basal arms, with one type of large inflated 

 thin-walled filaments or with stout primary filaments bearing fine secondaries. Pupal abdomen 

 with the normal pair of hooks each side ventrally on segment 5. Cocoon with neck. Postgenal 

 cleft pentagonal, subcordate or truncate-sagittate. Hypostomial teeth normal (Text-figs. 278 & 

 279), 4-10 (usually 6-8) setae in hypostomial row. Larval thoracic cuticle bare, abdominal 

 cuticle with minute sparse spinous hairs. Larval abdomen usually expanded gradually when 

 seen in profile and contracting suddenly to posterior circlet (Text-fig. 226). 



This is the largest species-group of Metomphalus and contains several forms 

 characteristic of high-altitude mountain streams, often occurring together with 

 species of subgenus Anasolen in swift cold cascades. The species are rather uniform 

 in the males (including male genital characters), females, and larvae, but the pupal 

 gill shows throughout the group a transition from forms with the filaments of two 

 quite distinct kinds (stiff dark primary branches and slender thread-like secondary 

 filaments) to forms with a single kind of thin-walled dilated filament — generally 

 somewhat sausage-like or banana-like. The larval head is usually strongly pig- 

 mented, sometimes to such an extent that the dark head-spots are almost lost among 

 the general dark brown infuscation, and the postgenal cleft is very conspicuous (in 

 some forms a lightly pigmented area extends forwards medially from the cleft to 

 the base of the hypostomium, making it appear as though the cleft itself is drawn 

 out anteriorly). The general appearance of the larvae is closely similar to that of 

 Anasolen larvae, but the small postgenal cleft in the latter distinguishes them from 

 larvae of the medusaeforme-group ; larvae are less easy to distinguish from those of 

 the subgenus Freemanellum, but appear to be consistently separable in the two 

 groups by the brush structure of the apex of the mandible (cf. Text-figs. 294 and 

 295). A striking larval mandibular feature in many species of the medusaeforme- 

 group is the unusual elongation of the distal one of the pair of serrations (as shown 

 in Text-fig. 300), a character found particularly in vorax and its immediate allies. 

 A remarkable feature of these species, not found in other Ethiopian Simulium, is the 

 presence of small but distinct teeth in the female cibarium. 



Two species of the medusaeforme-group (S. letabum and 5. natalense, possibly 

 also S. fragai) have the pleural membrane haired and thereby differ from other 

 Metomphalus species, and a few species of the group (mainly S. vorax and allies) have 



