SIMULIIDAE OF AFRICA 55 



irregularities on mandibular edge ; primary brush very small, not extending beyond apex of 

 mandible. Maxilla (Text-fig. 329) with small dark palp about two and a half times as long as its 

 basal width ; outer dorsal hair-tuft small and very inconspicuous, composed of only a few stiff 

 colourless setae. Cephalic fans (Text-fig. 325) forming curved brushes when open, but of excep- 

 tional form, with only about 14-18 rays of two types, outer rays at each end of the series small 

 fine and very pale but middle six or seven rays extremely large, stiff and black or brownish 

 black, the enlarged rays very conspicuous and widely separated from each other in the opened 

 fan ; all rays with filter-apparatus ; inner secondary fan flat and triangular when open with the 

 tips of the rays forming a straight line (as in Prosimulium). Thorax : Cuticle coarsely shagreened 

 dorsally and lightly sclerotized yellowish brown, colour appearing dark greyish laterally except 

 for milky cervical area, proleg whitish. Bare or with a few scattered dark setae of irregular size 

 similar to those on the abdomen ; proleg normally bare, sometimes very sparse minute simple 

 colourless hairs near base present. Spiracular scars black, very conspicuous. Proleg plates 

 very lightly sclerotized, with about 16 strong simple processes arising individually ; proleg circlet 

 with about 30-40 rows of 8-12 hooks. Abdomen : Body shape normal,' gradually expanding 

 towards penultimate segment, then contracting to circlet, segmentation unusually well marked 

 by constrictions intersegmentally, segmental spiracular scars black and very conspicuous ; 

 colour dark brownish dorsally and pale greyish ventrally, venter milky white at junctions of 

 segments. Cuticle with tough appearance, more or less smooth ventrally but coarsely shagreened 

 dorsally and dorsolaterally, the microsculpture formed by deep Assuring with raised areas 

 between the fissures, the raised areas mainly rounded dorsally (Text-fig. 319) but more elongate 

 dorsolaterally so that these areas appear slightly striate ; cuticle in addition to shagreenation 

 covered with dark setae on the dorsal surface, the setae conspicuous under low-power magnifica- 

 tion and of different sizes, the large blunt setae occurring mainly on posterior half of abdomen 

 being intermixed with smaller more spinous setae (Text-fig. 319) ; extent of distribution of setae 

 variable, some specimens with few or none anteriorly on abdomen, others with closer cover of 

 setae over thorax as well as abdomen, some specimens with setae extending well round sides of 

 abdomen ; dorsolateral expansions of last segment (laterad of anal sclerite) with large long pale 

 tapering setae. Ventral papillae absent, but sides of last segment swollen out and convex in 

 dorsal view (Text-fig. 318). Accessory sclerites undeveloped. Rectal gills simple, each lobe 

 bluntly rounded and without secondary lobules (Text-fig. 320), lobes milky white without pat- 

 tern. Rectal scales not seen, apparently absent. Anal sclerite normal X-shape, well sclerot- 

 ized. Posterior circlet with about 95-125 rows of 8-13 hooks. 



Material examined. Note : the <$ and $ specimens listed are pharate adults 

 dissected from pupae and preserved in alcohol. 



Holotype <$. St. Helena Island (South Atlantic) : Sandy Bay, 5.1.1963 {A. 

 Loveridge). In British Museum (Natural History), London. 



Paratypes*. St. Helena Island : 2 <J, 2 $, 27 pupae, 24 larvae, Sandy Bay, 

 29.xii.1962 (A. Loveridge) ; 1 <$, 6 pupae, Sandy Bay, 5. i. 1963 {A. Loveridge) ; 1 

 pupa, 4 larvae, Sandy Bay, 10.xi.1961 {A. Loveridge). All paratype material in 

 British Museum (Natural History), London, except for two larvae and two pupae 

 deposited in United States National Museum, Washington and two larvae and two 

 pupae deposited in Museum National d'Histoire Naturelle, Paris. 



Habitat. Simulium (Dexomyia) atlanticum sp. n. is so far known only from the 

 lower reaches of a single stream on the southern side of St. Helena, where sparsely 

 distributed larvae and pupae were found by Mr. Arthur Loveridge on large stones, 

 sometimes in the same stretches of stream where the immature stages occur of 

 Simulium {Eusimulium) loveridgei Crosskey (the only other Simuliid found on St. 



* See Appendix 



