On 1856 October 22nd Australia Gold Sovereigns and Half Sovereigns were legalised for use in Ceylon by Proclamation of Queen Victoria. It was revoked by proclamation on 1869 June 18th with the introduction of Decimal currency for Ceylon.
The 1856 October 16th Proclamation of Queen Victoria was only published in The Ceylon Government Gazette No. 3,044 of July 25, 1857;
The 1857 to 1866 Australia Sovereigns had Second Type of head engraved by L. C. Wyon. Older 1855 and 1856 Sovereigns of First Type, had larger head engraved by James Wyon, as used in the Sovereign Minted in London.
See discussion in Australia Sovereign coin
Ref: The Gold Sovereign. by M. A. Marsh.
1999, Cambridge U.K., 2nd ed. 118pp. Illustr. colour
The Australia Half Sovereign was scanned at 600 dpi and displayed at 300 dpi It was won on eBay in 1999 May.