In this work twenty-six species of the camaenid land snail Amplirhagada, which is endemic to the Kimberley region in Western Australia, are newly described. In addition, the anatomy of two further species, A. katerana and A. combeana, is described and a further, yet undescribed species is reported from Boongaree Island based on dry shell material. Most of these species occur on islands of the Bonaparte Archipelago off the mainland coast. The patterns of distribution and differentiation of these island species are comparable, however, with those found on the mainland. Mainland species are usually restricted to single rainforest patches. Frequently, single patches harbour only one or two congeneric species. Similarly, smaller islands usually support one endemic Amplirhagada species whereas on larger islands up to four species are found to occur in sympatry. Species are distinguishable particularly by the characteristic anatomy of the inner penial wall. Sympatric species generally exhibit marked morphological differences in shells and genital anatomy. A molecular phylogeny based on partial sequences of the mitochondrial cytochrome c oxidase unit 1 gene (COI) reveals a basal polytomy among species of the genus, which are generally genetically well differentiated. Relationships among species in the molecular tree mainly reflect geographical patterns.