Shell ovate to broadly conical; sutures slightly to well impressed; body whorl convex to strongly keeled, smooth. Operculum flat, paucispiral, yellow, with a white smear and 2–5 (typically 2–3) weakly developed pegs on inner surface. Radula with 3–4 (typically 4) basal cusps on central teeth. Penis simple, tapering; prostate gland closed, more or less kidney-shaped, with pallial vas deferens emerging from just before pallial wall on ventral side. Female genital system with simple, inverted U-shaped proximal coiled oviduct and short distal coiled oviduct with single bend. Pallial oviduct with opening overlapping anterior end of capsule gland.
Genus Posticobia Iredale, 1943
Type locality: In freshwater creek, Clarence River, New South Wales.
Inhabits freshwater springs, streams, rivers, and lakes down to the freshwater-brackish water interface. Found on stones, wood or roots. Can reach very high population densities. Egg capsules are small (0.3–0.4 mm in diameter) and hemispherical. Eggs are found attached to sand grains, vegetation or, rarely, to the shell of other molluscs.
Posticobia is found in a wide range of habitats. from isolated springs in central Australia to the large coastal rivers and lakes of New South Wales, Queensland and Norfolk Island.
Posticobia is genetically and anatomically closely related to Austropyrgus.
Beesley, P. L., Ross, G. J. B. and Wells, A. (Eds). 1998. Mollusca: The Southern Synthesis. Fauna of Australia. Vol. 5. CSIRO Publishing, Melbourne. Part A. Pp. i-xvi,1-563, Part B i-viii, 565-1234.
Clark, S. A. (2009). The genus Posticobia (Mollusca: Caenogastropoda: Rissooidea: Hydrobiidae SL) from Australia and Norfolk Island. Malacologia 51: 319-341.
Clark, S. A., Miller, A. C. & Ponder, W. F. (2003). Revision of the snail genus Austropyrgus (Gastropoda: Hydrobiidae): a morphostatic radiation of freshwater gastropods in southeastern Australia. Records of the Australian Museum 28: 1–109.
Ponder, W. F. (1981). Posticobia norfolkensis (Sykes), an apparently extinct fresh-water snail from Norfolk Island, Australia (Gastropoda, Hydrobiidae). Proceedings of the Linnean Society of New South Wales 105: 17-21.
Iredale, T. (1943). A basic list of the fresh water Mollusca of Australia. Australian Zoologist 10: 188-230.
Smith, B. J. (1992). Non-marine Mollusca. Pp. i-xii, 1-408 in W. W. K. Houston. Zoological Catalogue of Australia, 8. Canberra, Australian Government Publishing Service.
Smith, B. J. & Kershaw, R. C. (1979). Field guide to the non-marine Molluscs of South-eastern Australia. Canberra, A.N.U. Press.