SIMULIIDAE OF AFRICA 47 



the Sahara in which the radius is bare basally, isolation has certainly been less 

 complete and the valley of the Nile provides a linking route of almost continuous 

 distribution from Europe via the Middle East (where a species of Byssodon occurs at 

 least in the Tigris and Jordan valleys) to Egypt and the Sudanese Nile and hence to 

 Ethiopian Africa : a group of Simuliidae able to utilize the fluvial habitat provided 

 by the Nile itself would be able to disperse between the Palaearctic and Ethiopian 

 Regions at periods such as recent geological times when conditions of extreme 

 drought over wide areas imposed severe barriers against the dispersal of most forms. 

 The existence of the Nile is tentatively suggested as the explanation for the 

 occurrence of Byssodon segregate in both Africa and Eurasia, a group otherwise so 

 disjunct from the other elements in the Ethiopian fauna (excepting perhaps Afro- 

 simulium q.v.). 



The Middle Eastern species of Byssodon cited above is Simulium (Byssodon) 

 buxtoni Austen from Palestine and Iraq. This very small species in which the 

 scutum of the female has a pair of anterior rounded black-brown spots (figured by 

 Crosskey, 19676 : n) is unfortunately still known only from the adult female, but 

 the genital fork and all other characters confirm its position in Byssodon. In an 

 earlier paper (Crosskey, 19676) I assigned the species, under the name irakae Smart, 

 to Psilocnetha but since this genus-group name is here sunk to Byssodon the Middle 

 Eastern species is re-assigned accordingly. Dr. Alan Stone (personal communica- 

 tion) has very kindly pointed out to me that Smart (1944) did not need to provide 

 his replacement name irakae for the preoccupied Simulium bipunctatum Austen 

 because S. bipunctatum var. buxtoni Austeni was held to be conspecific with typical 

 bipunctatum and the species-group name buxtoni was therefore nomenclaturally 

 available for the species concerned : the species referred to as irakae Smart in my 

 previous paper (Crosskey, 1967b) should be known under the rules of nomenclature 

 as buxtoni Austen, and irakae Smart falls as a junior synonym of this name. 



Simulium transiens Rubzov from Siberia and Canada has been assigned to 

 Byssodon by Rubzov (1940, 1959-1964 : 427) and by Stone (1965), but Rubzov 

 (1959-1964 : 623) erected the genus Parabyssodon Rubzov, 1964 as a monotypic 

 genus for this species. I have examined adult, pupal and larval material of transiens 

 and consider it best at the present time to accept Parabyssodon as a subgenus of 

 Simulium distinct from Byssodon, although it must be admitted that the larva is 

 extraordinarily closely similar to that of the African griseicolle-gvoup of Byssodon, 

 the larva of transiens having the same abdominal form and deeply divided fan- 

 shaped setae all over the dorsum of thorax and abdomen as griseicolle (i.e. without 

 the series of dorsolateral abdominal prominences and spatulate setae as occur in 

 Holarctic Byssodon). The Eusimulium-\\ke pupa of Parabyssodon with four slender 

 gill filaments projecting forwards is different from that of any Byssodon species, and 

 the dilated fore tarsus, male genital characters, and semi-shining female scutum of 

 Parabyssodon are also notable differences. 



Stone (1965) assigns S. rugglesi Nicholson & Mickel and S. slossonae Dyar & 

 Shannon to subgenus Byssodon, but rugglesi, with its male ventral plate, style shape, 

 and postgenal cleft shape is possibly closer in its characters to Simulium s. str. 



