The Australian species of the water beetle genus Hydraena Kugelann, 1794, are revised, based on the study of 7,654 specimens. The 29 previously named species are redescribed, and 56 new species are described. The species are placed in 24 species groups. High resolution digital images of all primary types are presented (online version in color), and geographic distributions are mapped. Male genitalia, representative female terminal abdominal segments and representative spermathecae are illustrated. Australian Hydraena are typically found in sandy/gravelly stream margins, often in association with streamside litter; some species are primarily pond dwelling, a few species are humicolous, and one species may be subterranean. The areas of endemicity and species richness coincide quite closely with the Bassian, Torresian, and Timorian biogeographic subregions. Eleven species are shared between the Bassian and Torresian subregions, and twelve are shared between the Torresian and Timorian subregions. Only one species, H. impercepta Zwick, is known to be found in both Australia and Papua New Guinea. One Australian species, H. ambiflagellata, is also known from New Zealand. New species of Hydraena are: H. affirmata (Queensland, Palmerston National Park, Learmouth Creek), H. ambiosina (Queensland, 7 km NE of Tolga), H. antaria (New South Wales, Bruxner Flora Reserve), H. appetita (New South Wales, 14 km W Delagate), H. arcta (Western Australia, Synnot Creek), H. ascensa (Queensland, Rocky Creek, Kennedy Hwy.), H. athertonica (Queensland, Davies Creek), H. australula (Western Australia, Synnot Creek), H. bidefensa (New South Wales, Bruxner Flora Reserve), H. biimpressa (Queensland, 19.5 km ESE Mareeba), H. capacis (New South Wales, Unumgar State Forest, near Grevillia), H. capetribensis (Queensland, Cape Tribulation area), H. converga (Northern Territory, Roderick Creek, Gregory National Park), H. cubista (Western Australia, Mining Camp, Mitchell Plateau), H. cultrata (New South Wales, Bruxner Flora Reserve), H. cunninghamensis (Queensland, Main Range National Park, Cunningham's Gap, Gap Creek), H. darwini (Northern Territory, Darwin), H. deliquesca (Queensland, 5 km E Wallaman Falls), H. disparamera (Queensland, Cape Hillsborough), H. dorrigoensis (New South Wales, Dorrigo National Park, Rosewood Creek, upstream from Coachwood Falls), H. ferethula (Northern Territory, Cooper Creek, 19 km E by S of Mt. Borradaile), H. finniganensis (Queensland, Gap Creek, 5 km ESE Mt. Finnigan), H. forticollis (Western Australia, 4 km W of King Cascade), H. fundaequalis (Victoria, Simpson Creek, 12 km SW Orbost), H. fundata (Queensland, Hann Tableland, 13 km WNW Mareeba), H. hypipamee (Queensland, Mt. Hypipamee National Park, 14 km SW Malanda), H. inancala (Queensland, Girraween National Park, Bald Rock Creek at "Under-ground Creek"), H. innuda (Western Australia, Mitchell Plateau, 16 mi. N Amax Camp), H. intraangulata (Queensland, Leo Creek Mine, McIlwrath Range, E of Coen), H. invicta (New South Wales, Sydney), H. kakadu (Northern Territory, Kakadu National Park, Gubara), H. larsoni (Queensland, Windsor Tablelands), H. latisoror (Queensland, Lamington National Park, stream at head of Moran's Falls), H. luminicollis (Queensland, Lamington National Park, stream at head of Moran's Falls), H. metzeni (Queensland, 15 km NE Mareeba), H. millerorum (Victoria, Traralgon Creek, 0.2 km N 'Hogg Bridge', 5.0 km NNW Balook), H. miniretia (Queensland, Mt. Hypipamee National Park, 14 km SW Malanda), H. mitchellensis (Western Australia, 4 km SbyW Mining Camp, Mitchell Plateau), H. monteithi (Queensland, Thornton Peak, 11 km NE Daintree), H. parciplumea (Northern Territory, McArthur River, 80 km SW of Borroloola), H. porchi (Victoria, Kangaroo Creek on Springhill Rd., 5.8 km E Glenlyon), H. pugillista (Queensland, 7 km N Mt. Spurgeon), H. queenslandica (Queensland, Laceys Creek, 10 km SE El Arish), H. reticuloides (Queensland, 3 km ENE of Mt. Tozer), H. reticulositis (Western Australia, Mining Camp, Mitchell Plateau), H. revelovela (Northern Territory, Kakadu National Park, GungurulLookout), H. spinissima (Queensland, Main Range National Park, Cunningham's Gap, Gap Creek), H. storeyi (Queensland, Cow Bay, N of Daintree River), H. tenuisella (Queensland, 3 km W of Batavia Downs), H. tenuisoror (Australian Capital Territory, Wombat Creek, 6 km NE of Piccadilly Circus), H. textila (Queensland, Laceys Creek, 10 km SE El Arish), H. tridisca (Queensland, Mt. Hemmant), H. triloba (Queensland, Mulgrave River, Goldsborough Road Crossing), H. wattsi (Northern Territory, Holmes Jungle, 11 km NE by E of Darwin), H. weiri (Western Australia, 14 km SbyE Kalumburu Mission), H. zwicki (Queensland, Clacherty Road, via Julatten).
TWO NEW SPECIES OF TENUIPALPUS DONNADIEU FROM NEW SOUTH WALES (ACARI: TENUIPALPIDAE)
