SCIENTIFIC INTEREST AND POTENTIAL VALUE Land snails have long been favourite subjects of study for biologists, as they are slow moving and easy to catch, are easily marked and are generally tolerant of laboratory conditions. They have been used extensively for research into the basis of natural selection, on account of the high degree of diversity found both within and between populations. Some of the strongest evidence that natural selection acts on genetically determined visible characters has been produced from studies on land snails such as Partula (see review)f5). Land snails are also important subjects of study for biogeographers, providing evidence for theories on the distribution of land masses and species (16). Terrestrial molluscs play an important ecological role. They dispose of large quantities of dead plant matter and provide food for a wide variety of animals (25). Compared with marine molluscs, their use as food by man is fairly small, but in several countries snails are considered a gastronomic delicacy. Helix pomatia is famous for its role in French cooking (see review) but other species such as Helix aspersa and increasingly Achatina fulica the Giant African Snail, are also eaten in large quantities. Taiwan is now a major exporter of the latter (34). Shell collectors have recently become interested in land snails, particularly the colourful tree species. Liguus virgineus from Haiti, L. fasciatus from Florida, Polymita from Cuba and a wide variety of species from the Philippines and Papua New Guinea are involved in the international shell trade (26,27,28). THREATS TO SURVIVAL Land snails include some of the most vulnerable terrestrial invertebrates, and many species have become extinct over the last century. This is particularly apparent on Pacific islands. The unbalanced nature of the original fauna arriving on such islands and the subsequent lack of immediate competition often results in the development of very delicately balanced communities which can be easily disturbed. The degree of land snail extinction in the outer islands of Polynesia (Rapa Island, Marquesas, Mangareva, the Hawaiian Chain and the Austral Group) has been described as catastrophic (15). By 193f, the land snail fauna of Mangareva was reduced to a single forest patch; Rapa Island probably lost 50 per cent of its endemic species between 193 and the mid-1960s; and very few endemic species were found in the Marquesas or on Kauai in the 1970s. In the Society and Samoan Islands ground-dwelling taxa are fast becoming extinct (15). In Hawaii, of approximately 1061 endemic snail species, about 600 have probably become extinct recently and another 200-t00 are probably endangered (10). Many species in the family Achatinellidae are seriously endangered. The subfamily Achatinellinae of approximately 100 species is endemic to Hawaii and provides a good example of the rapid decline of this group. Recent searches have failed to find many species in the four genera, Achatinella (see review), Partulina Perdicella and Newcombia No trace of Hawaii Island's three Partulina species have been found recently; Oahu's only Partulina has not been found for decades; on Molokai only five of the eight species have been found recently, most of which were very rare and local; and Lanai has only two or three Partulina species in the small amount of remnant native forest. On Molokai only one living individual of the island's sole Perdicella species has been found recently (8,56). All members of the Partulidae are probably threatened (see review for Moorean species) and the Short Samoan Tree Snail Samoana abbreviata may now be extinct. In 1926 this species was abundant and widely distributed on Tutuila but despite strenuous efforts it was not collected in 1975 (16). In the Pacific, more than 100 species in the family Endodontidae have become extinct within the last 50 years (35). In the 1830s, 13 species were collected on Rarotonga in the Cook Islands but in 1965 only two were found. In the 18tos living endodontoids were recorded from Mangareva in the Gambler Islands but in 193> only the dead remains 158