Very interesting, not really sure which species this is. Pretty sure it belongs to the genus Parmavitrina but which species I am not sure. Parmavitrina rubrica (Shea and Griffiths, 2010) is found in that general area however it has a brick red coloured animal not black. I once found a similar large black coloured semi slug at Yarrahappinni which is within the range of Parmavitrina planilabris found on the mid north coast of NSW. It is possible that the snails in the Parmavitrina genus may have more than one colour form within species populations. That is the best I can do I am afraid. Just a request Warrigal/Trevor, could you please post this in the 'Snails of Australasia' Facebook group ? that way we could get some more feedback and identification suggestions. Cheers, Michael