Distribution and size of Gulella viae Bnp. and G. contraria Conn., two South African streptaxids (Gastropoda Pulmonata)

The Drakensberg range, forming an interrupted eastern escarpment in South Africa and further north, is covered with various types of forest on its eastern ( = wet) slopes. These forests harbour a rich assemblage of land molluscs displaying different patterns of distribution. Normally one would expect the escarpment species to be distributed from the interrupted eastern Cape Province mountains to the almost continuous Natal range with further north again scattered occurrence in Swaziland (a poorly collected country) and the eastern Transvaal, with occasional distribution northward in the eastern escarpment on the borders of Zimbabwe (formerly Rhodesia) and Mozambique. Where the range is discontinuous such as in the eastern Cape Province and Transvaal, more or less well-marked endemism may occur and where the interval is of major historical/ecological significance, such as the ancient and arid Limpopo River valley, it may act as a biogeographical barrier. The detailed distribution of the majority of southern African land gastropods is unknown; although many patterns have emerged, these should be considered with suspicion and a number of these have already been emended by newly collected material. Some patterns may reflect collecting activity rather than natural distributions. This may particularly apply to the Natal mountainous areas, which have been well investigated by Henry Clifden Burnup (1852-1928) and his associates; most of this material has been deposited in the Natal Museum at Pietermaritzburg, where Burnup was honorary curator of molluscs in the years 1904-1928. Collecting activities by the present author in the Transvaal in the period 1962-1966 have revealed that a number of the Natal Drakensberg species also occur in the Transvaal escarpment forests and are in fact only limited in their distribution by the low-lying and arid Limpopo River valley.