Abstract
Species of Meridolum Iredale, 1942 have previously been recognised as occurring from southern Queensland south along the New South Wales coast and coastal ranges to eastern Victoria, and are characterised by subglobose to depressed helicoid shells that range in size from about 10–33 mm in height and 15–39 mm in diameter. The genus was thought to contain a small number of widespread species, with the main radiation centred within 200 km of Sydney, central New South Wales. Using a combination of morphological, anatomical and genetic markers the current study has revealed a remarkable diversity in shell morphology, reproductive anatomy and genetic structure. This study has resulted in the recognition of 22 species (seven new) allocated to five genera (four new). Most species have narrow ranges with four only known from their type locations. One species, Meridolum corneovirens (Pfeiffer, 1851), has been listed as endangered, but several more species in the complex, probably from both Queensland and New South Wales, also merit listing.