On the distribution of the genus Xerocerastus Kobelt & Von Möllendorff, 1902 (Mollusca, Gastropoda Pulmonata, Subulinidae)

Opgedragen aan Prof. Dr. H. Boschma ter gelegenheid van zijn 70ste verjaardag. The subfamily Rumininae of the pulmonate gastropod family Subulinidae is represented in Southern Africa by the endemic genus Xerocerastus Kobelt & von Möllendorff, 1902. Xerocerastus has been divided into three subgenera, viz., Xerocerastus s.s., Lubricetta Haas, 1928 and Namibiella Zilch, 1954 ¹). About fourteen species with many varieties, of which most are probably only of ecological significance, are now generally recognized. The genus is not treated in Connolly's monograph (1939), but the group has been reported upon in detail by various authors, viz., Connolly (1930), Zilch (1939, 1954) and Van Bruggen (1963). A number of years ago my attention was drawn to a sample of Xerocerastus burchelli (Gray) from the Northern Transvaal, preserved in the Rijksmuseum van Natuurlijke Historie, Leiden; this seemed outside the known range of both genus and species and the case was filed for further investigation. Only recently I have had opportunity to go into this matter and the results of this study are presented here. Pilsbry (1919, pp. 309-310, fig. 158) was the first to discuss distribution and affinities of the genus Xerocerastus. Degner's (1923) studies of the anatomy showed that, contrary to general opinion, Xerocerastus does not belong to the Enidae, but must be referred to the family Subulinidae of the superfamily Achatinacea (c.q. Achatinidae s.l.). Consequently in showing the distribution of Xerocerastus as a subgenus of Cerastus, and in connection with the range of the latter, Pilsbry's map has to a certain extent lost its meaning. The genus Xerocerastus has to be considered an isolated element