We investigated patterns in species richness and similarity in species composition of land snail communities in relation to biogeographic and environmental gradients on continental islands along the Kimberley coastline of Western Australia. The camaenid land snails demonstrated high overall species richness, restricted geographical ranges (mostly to a single island) and almost complete turnover of species among islands. In comparison, the overall number of the smaller non-camaenid land snail species was much lower. They also had much wider distributions and a lower level of species turnover among islands. These results are consistent with the differing dispersal abilities of the two groups, one fostering in situ speciation and the other inter-island colonisation. We also show that dispersal ability was not the only driver of species richness and composition of land snail species on islands, but that rainfall, island area and availability of habitat also played a role. Rainfall was the major environmental driver of richness and composition for both groups of land snails. Rainfall was also highly correlated with extent of rainforest cover, habitat that provides a suitable micro-climate for snails and additional ecological niches compared to more open habitats.