Variety equivalents: 
Breen 1117

Rarity: Very Rare

Notes:
The obverse die of this variety was also used on:
1785 Machin's Mills - Vlack 15-85NY 
1785 Immune Columbia / Nova Constellatio, Pointed Rays, No Extra Star 
1785 Immune Columbia / Nova Constelatio, Blunt Rays

The reverse die of this variety was also used on:
1783 Nova Constellatio Copper - Crosby 2-B

Images courtesy of the National Numismatic Collection of the Smithsonian Institution

Varieties:
Copper 
Gold

On May 9, 1843, Matthew Stickney, a coin collector who could only be called "advanced" by today's standards, visited the United States Mint and traded a 1785 "Immune Columbia" Cent overstruck on a 1775 British gold Guinea (plus some other American Colonial coins) for an 1804 Silver Dollar.  Stickney claimed to have acquired the Immune Columbia from the New York bullion dealers, Beebee & Parshall, the day before.  The gold Immune Columbia still resides in the National Numismatic Collection at the Smithsonian Institution and no other has ever appeared on the market.  Stickney's 1804 Silver Dollar sold on April 6, 1997 for $1,815,000 as part of the Eliasberg collection and now resides in a PCGS Proof-65 holder in a private collection.

Sources and/or recommended reading (click on any active link to purchase that book):
"Walter Breen's Complete Encyclopedia of U.S. and Colonial Coins" by Walter Breen, p. 119

Auctions by Bowers and Merena, Inc., "The Walter H. Childs Collection" sale catalog, August 30, 1999, pp 110-111