SIMULIIDAE OF AFRICA 51 



(Text-fig. 69) they are not much wider than the postocular part of the head and in 

 dorsal view (Text-fig. 71) are much wider apart than normal : compare with the 

 profile and dorsal views of the female head in typical Simulium shown in Text-figs. 

 66 & 70. The female mouthparts, however, are toothed and presumably functional 

 for haematophagy (if so, the females if anautogenous must feed on avian blood since 

 St. Helena has no endemic mammalian fauna). 



The pupal gill form in S.(D.) atlanticum sp. n. is in no way specially remarkable 

 but the pupal cephalothorax is unusual among black-flies from the African area in 

 having a covering dorsally of strong small spinous tubercles (Text-fig. 321), rather 

 similar to those found in the subgenus Xenosimulium from Madagascar. The most 

 unique feature of the pupa, however, is the presence ventrally on segments 5-7 of 

 the abdomen of an irregular transverse row of about 14-18 strong hooks (Text-fig. 

 323) in place of the usual single spaced pair on each side of these segments ; the only 

 other members of the world fauna of Simulium known to me to have anything 

 similar is the mayfly-phoretic species Simulium (Phoretomyia) lumbwanum de 

 Meillon from East Africa in which the fifth to seventh pupal abdominal segments 

 are girdled with blunt black hooks (see Text-figs. 170 & 173) ; atlanticum does not 

 have strong hooks dorsally on these segments, but it does have (in addition to the 

 very reduced anterior spine-combs) two or three minute spinous-hooklets each side 

 dorsally on the posterior margins (Text-fig. 324), another unusual feature. 



The structure of the larval head in S.(D.) atlanticum sp. n. is superficially much 

 more like that of Prosimuliine black-flies than that of normal Simulium, and the 

 strongly bulbous sides of the head-capsule itself (Text-figs. 325 & 328) and the shape 

 of the cephalic apotome (broadest near the middle and then contracting towards the 

 hind margin of the head, Text-fig. 325) are just as in Prosimulium Roubaud, and the 

 shape of the hypostomium in some ways resembles that found in Stegoptema, 

 Gigantodax or even in Gymnopais or Twinnia. The resemblances to these Pro- 

 simuliine genera are, however, certainly due to convergence, for (apart from charac- 

 ters of the adults and pupae which confirm relationship to Simulium s.l. and not 

 Prosimuliini) there are more larval characters that conform to the Simuliine and 

 not to the Prosimuliine type ; for instance the mandible and its serrations, the very 

 weakly developed tuft of hairs near the base of the maxillary palp, the isolated 

 cervical sclerites, and the presence of setae on the thoracic and abdominal cuticle 

 (which is bare in the larvae of all Prosimuliini). Another presumably convergent 

 resemblance is that of the larval hypostomium (Text-fig. 326) to the hypostomium 

 found in some species of the African subgenus Phoretomyia that attach to nymphal 

 mayflies : there is the same tendency to formation of paired outer groups of five 

 blunt apical teeth, with a sunken or isolated middle group of one or three teeth, as 

 exists in the copleyi-group (Text-fig. 266) and the berneri-group (Text-fig. 267) ; 

 furthermore atlanticum resembles the copleyi-group in the shape of the cephalic 

 apotome (cf. Text-figs. 286 and 325) and in cranial convexity. 



The cephalic fans of Dexomyia differ from those of all other black-flies by having 

 the main curved rays of two distinct types, some of them slender and pale, and a few 

 of them (usually numbering six or seven in each fan) exceptionally heavily sclero- 



