The Ninth Galaxy was a galaxy that was part of the Twelve Galaxies circa 2000000. It contained the planet Svartos. (PROSE: Dragonfire)
When the Sixth Doctor initially thought he and Charlotte Pollard landed on the planet Spiridon, he stated it was in the ninth system of "a far away galaxy", later called the "ninth galaxy" and later the "galaxy of Antares". (AUDIO: Brotherhood of the Daleks)