An imaginary inland sea in Australia

Alan Day narrates in his book The A to Z of the Discovery and Exploration of Australia the following about a curious map of Australia dating from the early 19th century:

The Friend of Australia [is a book] attributed to a Retired Officer of the Hon. East India Company’s Service, now known to be a Mr. Thomas J. Maslen. The Friend of Australia (1830) combined the principal unexplored inlets and other topographical features round Australia’s coastline (…). Maslen was not shy aboutrecommending named individuals to be entrusted with the exploration of different regions. Should an inland sea be discovered, then Captain Bayfield and Lieutenant Fraser, the surveyors of the Canadian Lakes, should be sent to determine its length, breadth, and course. A fold-out map Sketch of the Coasts of Australia and of the supposed Entrance of the Great River together with accompanying notes, adds much to the book’s interest. Some unfamiliar and speculative geographical names appear…

Australia inland sea