Type species: Hydromys chrysogaster E. Geoffroy, 1804.

Content: With the exclusion of Baiyankamys, I recognize four described species of Hydromys as valid: H. chrysogaster, with synonyms as delineated by Tate (1951b) and Musser and Carleton (2005), widely distributed in river systems and coastal areas of Tasmania, Australia, and many adjacent islands on the continental shelf, and in the lowlands of New Guinea (to 2000 m) and on immediately adjacent islands (Yapen, Biak­Supiori, Waigeo, the Aru and Kai Islands, and the D’Entrecasteaux and Trobriand Islands); H. neobrittanicus Tate and Archbold, 1935, a distinctive, large­bodied insular endemic from the large island of New Britain in the Bismarck Archipelago; H. hussoni Musser and Piik, 1982, known only from the Wissel Lakes of western New Guinea; and H. ziegleri n. sp., from foothills on the southern margins of the Prince Alexander Range in northern Papua New Guinea. There is one additional undescribed species, endemic to the island of Obi in the North­Central Moluccas (Helgen 2003; Musser and Carleton 2005).