Two new species of subterranean Dytiscidae, Phreatodessus hades and Kuschelydrus phreaticus, are described from New Zealand. They are compared with Siettitia balsetensis Abeille de Perrin from France and Morimotoa phreatica Uéno from Japan, all 4 being referable to tribe Bidessini. General morphology is discussed and, because sclerotised parts of the reproductive systems of both sexes are likely to show the most significant evidence of phylogenetic relationships, genitalia drawings are given of all 4 species to facilitate comparison. This in turn has led to consideration of the possible evolution of the spermatheca, the most primitive form of which is seen in Phreatodessus hades. Brief consideration is given to distribution, seasonal occurrence, and habitat.