This is one of two 1876 transitional double eagles. This design has the obverse of 1877 with the top of Liberty's diadem centered between stars six and seven combined with the reverse design of 1877 and beyond with 'Dollars' fully spelled out. The obverse dies prior to 1877 have Liberty's coronet virtually touching star seven.
This particular example, with a plain edge, was struck from a different obverse die than the others using this reverse J1490-J1491/P1643-P1644. It has the date very close to the tip of Liberty's bust and was probably the first die made with this star arrangement. It was then rejected after this trial strike was made.
The illustrated example is unique and is ex Col Green, Boyd (BGJ 1/4/44 invoice $150), Farouk, Kreisberg-Schulman 2/60, Kagin's 11/64, RARCOA 5/71, HIM 11/82, 1995 ANA, Heritage 1/04, Superior 5/06 as PCGS64, Simpson collection - PCGS63 gilt.
Photo courtesy of PCGS.