Land snail faunas of the Deserta Islands, Madeiran archipelago, past and present.

Results of three recent surveys of the land snails of the Deserta Islands, Madeiran archipelago are given, including a newly described fossil fauna on the largest island, Deserta Grande. Age estimates on shells from the sediments suggest deposition between 60,000 and 90,000 yr BP. Results are compared with 19th century records, and with similar undated fossil material from the island of Bugio, known since the 19th century. A revised annotated check-list of records is provided. The Pleistocene faunas include species now extinct on the islands, indicative of wetter and better vegetated conditions than now. The two largest islands have suffered considerable environmental degradation since their discovery, and show apparent rates of extinction over the last 150 yr much greater than in the larger islands of the archipelago, Madeira and Porto Santo. The Desertan land snail fauna is much closer to that of Madeira than that of Porto Santo, reflecting an earlier probable land connection.