A new subfamily, Horelophopsinae subfam. nov., of Hydrophilidae is established for a remarkable new genus and species, Horelophopsis avita gen. nov., sp. nov., from Irian Jaya (New Guinea). It is assumed to represein the sister group of the two main subfamilies of Hydrophilidae (Hydrophilinae + Sphaeridiinae). The state of knowledge of New Guinean Hydrophilidae is briefly summarized.