STREPTAXIDAE (MOLLUSCA, GASTROPODA: PULMONATA) FROM ALDABRA ISLAND, WESTERN INDIAN OCEAN By A. C. VAN BRUGGEN INTRODUCTION THE pulmonate gastropod family Streptaxidae has an almost circumtropical distribution. Species are particularly numerous and diverse on the African con-tinent ; in addition the family is well represented on Madagascar, the Comoros, Seychelles and Mascarene Islands in the Western Indian Ocean. Aldabra atoll (924' S 462o' E) is situated in the southwestern Indian Ocean (fig. 5) ; the nearest land of any magnitude is the island of Madagascar at a distance of about 420 km to the southeast and the African mainland at about 640 km to the west. Apart from very small atolls the nearest high islands are the Comoros at a distance of about 400 km to the southwest. The Seychelles are further away than both the African continent and Madagascar, viz. about 1200 km to the northeast. Maxwell Smith (1909) was the first to record the presence of streptaxids on the island of Aldabra. Messrs J. F. Peake and J. D. Taylor have been participating in various phases of the Royal Society Expedition to Aldabra. In the course of their work on the atoll and its satellite island Assumption they have collected extensive series of streptaxid shells, the study of which they have entrusted to the present author. Aldabra and Assumption appear to harbour four species of Streptaxidae, three of which are extinct. All are described below followed by a discussion on their relationships and possible derivation. The following abbreviations have been used : BMNH British Museum (Natural History), London ; NM Natal Museum, Pietermaritzburg ; PSTE/JCFF Percy Sladen Trust Expedition, leg. J. C. F. Fryer ; RMNH Rijksmuseum van Natuurlijke Historic, Leiden ; RSE Royal Society Expedition ; lid ratio length/major diameter of shells. The l/d has been calculated from micrometer readings, so that these figures may not always agree with those calculated from the accompanying measurements in mm. Acknowledgements are due to Mr J. F. Peake and Dr J. D. Taylor, and the staff of the Mollusca Section of the British Museum (Natural History) for assistance in various respects. I am also indebted to The Royal Society, who have fostered and encouraged research on Aldabra Island. Thanks are due to Dr A. Zilch of the Senckenberg-Museum, Frankfurt am Main, for hospitality for comparative studies at his institute, and to Mr R. N. Kilburn of the Natal Museum for lending the Bull. Br. Mus. nat. Hist. (Zool.) 28, 5 Issued 17 September, 1975
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