This is a restrike, made in the 1870s, using the obverse design originally used on J93-J94/P105-P106 combined with his flying eagle reverse used on several patterns in 1838. The obverse is similar to the one used on 1838 eagles just facing the other way. It shows rust and the reverse die is heavily cracked.
It is attributed to Gobrecht in the original editions of Judd but a July 12, 1843 letter from W.E. Dubois to Matthew Stickney in the Peabody Essex Museum attributes this design to Kneass as noted below.
"One half dollar of 1839, of a die which you never saw before, nor did I, until today. This die was made by Mr. Kneass, the late engraver, since deceased. A very few pieces were struck; I don't think I could get another, except for the Cabinet, where there is none as yet".
The following 2 are confirmed:
1) Parmelee, Byron Reed-Durham Museum - ICG63, darkly toned as are many of their silver pieces, illustrated above.
2) Woodin, Newcomer, Boyd, Farouk, Judd, Krouner, Coronet Coin, Witham-Auction 81, Harry W. Bass Jr. Research Foundation. To view, click here.
An example, struck in copper J92/P102 is mentioned in the reference books but its existence has not been confirmed.
Image from the Byron Reed Collection; owned by the City of Omaha, Nebraska; on loan to The Durham Museum.