SIMULIIDAE OF AFRICA 33 



horizontal plane and are hardly visible from posterior view of the head, the area 

 between them being widely membranous since the broad postgenal membrane area 

 extends ventrally as far as the ventral posterior edge of the head. 



The male head in Afrosimulium is exceptionally large in relation to body size, and 

 the relatively small occipital foramen is far removed from the top margin of the 

 head-capsule so that the occipital depression (between the foramen and the junction 

 of the holoptic eyes) is very deep (Text-fig. 58) ; on the other hand, the foramen of 

 the female head-capsule is centred above the mid-point of the head (Text-fig. 60). 

 In Simulium the occipital foramen of both sexes is situated in the centre of the 

 posterior surface of the head, and the occipital depression of the male between 

 foramen and eye-junction is much wider than its depth (Text-fig. 57). 



The head-capsule morphology is so homogeneous throughout the family Simuliidae 

 that the strikingly different adult head architecture found in Afrosimulium garie- 

 pense — quite unlike that of any other black-fly — is of outstanding interest, for it 

 suggests the possibility that the radical modification of head morphology is asso- 

 ciated with some unique biological purpose (at present nothing is known of the 

 behaviour of gariepense except that females will hover around man and livestock 

 without biting and that males may come to light). Here it is of interest to note 

 that the whole female proboscis of gariepense is much longer than is usual in Simuliids 

 (though not unlike the unusually long proboscis of Simulium rostratum Smart & 

 Clifford from New Guinea) and this may be functionally related to the horizontal 

 plane of the cardines and to the other modifications of the lower posterior part of the 

 head : the mouthparts themselves are normal for biting forms, and the possibility 

 exists that elongation of the proboscis (and changes of head morphology, if corre- 

 lated) are adaptations for feeding on an unusual host. There is no evident explana- 

 tion for megacephaly of the male. 



The calcipala in A. gariepense is a very small inconspicuous lobe (Text-fig. 306), 

 described in the diagnosis above for brevity as ' almost absent ' ; de Meillon (1953) 

 stated that it is absent, but there is clearly some development of a calcipala but not 

 like that of Simulium s.l. (although even among Simulium there are some forms, 

 such as the Neotropical Andean subgenus Pternaspatha Enderlein, in which the 

 calcipala is completely undeveloped). Three other characters may be briefly 

 mentioned : the last segment of the maxillary palp (Text-fig. 305) is short and sub- 

 cylindrical or slightly clubbed, about subequal in length to either the third or fourth 

 segments, and therefore differs from that of Simulium in which the last segment is 

 (with very rare exceptions) much longer than either of the two preceding segments 

 and usually tapering and sinuous. The fore leg is unusually slender, with the 

 basitarsus 9-10 times as long as its greatest width and with the tibia thinner than 

 normal (Text-fig. 307). The genital fork of the female terminalia is without the 

 slender forward thumb-like process on each arm that occurs in the superficially 

 similar females of Simulium subgenus Byssodon. 



Finally in this discussion of the characters of gariepense it should be emphasized 

 that the new genus Afrosimulium is erected for this species with some doubts as to 

 whether this is the most appropriate taxonomic treatment or not. Much depends 



