The so-called transitional half eagle with 'In God We Trust' on the reverse. This reverse was adopted in 1866.
This forms part of a set along with the eagle J449/P521 and double eagle J452/P524.
These are believed to have been struck in 1865 although they may also have been restruck in the early 1870s.
According to the June 1870 Mason & Co sale, two examples of this design were struck in gold J445/P517 one ex Woodin, Newcomer, Col Green and Boyd, Farouk and the illustrated piece in the Smithsonian which was acquired in 1892. It is unclear which piece was the one offered in the 1870 sale although traditionally it has been placed with the Farouk coin. I actually believe the Mint collection set was the one offered in 1870 and the Woodin set likely came from Snowden for returning the 2 1877 half eagles.
Over a dozen are known in copper J446/P518 several of which have been gilted. The first definite appearance of this design was in the April 1870 auction by John Haseltine of coins from the Idler collection. A possible earlier listing may be Cogan's September 1869 sale.
Photo courtesy of the National Numismatic Collection of the Smithsonian Institution.