Posticobia norfolkensis differs from P. brazieri in its general shell shape - the last whorl is sub-shouldered (a feature lacking in P. brazieri), it also lacks a keel on the last whorl. P. norfolkensis also differs in the number of cusps on the outer marginal teeth of the radula, 35-38 (25-35 in P. brazieri).
Posticobia norfolkensis (Sykes, 1900)
Class Gastropoda
Infraclass Caenogastropoda
Order Littorinida
Suborder Rissoidina
Superfamily Truncatelloidea
Family Tateidae
Genus Posticobia Iredale, 1943
Original name: Paludestrina norfolkensis Sykes, 1900. In Sykes, E. R. (1900). Notes on the non-marine Mollusca of Norfolk and Phillip Islands, with descriptions of new species.Proceedings of the Malacological Society of London 4: 139-147.
Type locality: Bumbora Beach, Norfolk Island.
Unknown, almost certainly extinct.
Norfolk Island.
Unfortunately, this species is believed to be extinct, as a considerable effort was made to recollect it without success in June 1979 and November 1997. Habitat destruction due to human intervention and damage caused by grazing cattle were indicated as major contributors to the demise of this species (Ponder, 1981).
Clark, S. A. (2009). The genus Posticobia (Mollusca: Caenogastropoda: Rissooidea: Hydrobiidae SL) from Australia and Norfolk Island. Malacologia 51: 319-341.
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.
