Charles E. Barber's famous 1891 Liberty half dollar pattern. This design as illustrated went into regular production the following year but with a different reverse without the clouds above the eagle. This particular reverse design was also used on a quarter dollar pattern J1761/P1975.
Although the Judd book says that 2 are known, this pattern is actually unique and is in the Smithsonian.
Photo courtesy of the National Numismatic Collection of the Smithsonian Institution.