Wikipedia
Half-union
The Half-Union (also known as J-1548) was a United States coin minted as a pattern, or a coin not approved for release, with a face value of fifty U.S. Dollars. It is often thought of as one of the most significant and well-known patterns in the history of the U.S. Mint. The basic design slightly modified the similar $20 "Liberty Head" Double Eagle, which was designed by James B. Longacre and minted from 1849 to 1907.