This is a reverse die trial, struck in gold, of the regular "Short Arrowheads" variety used from 1859-1866 according to Pollock.
It was offered as lot 469 in Lester Merkin's 10/73 sale and was described as follows:
"n.d. (1859) Uniface trial of new reverse for quarter eagles, probably the first proof die sunk from the new hub of that year. Differs from 1840-58 in shape of claws, arrowheads, and wingtips; heavier pendants to T's, etc., these features continuing to 1907. Struck on oversize round gold blank with plain edge, wt. 79 1/2 grains (!). Brill. Proof. On the blank outer margin is III (chisel marks?); on blank rev. at rim directly opposite III is incuse O O, from punches; significance unknown. Unpublished Unique."
Photo is a scan from the Merkin 10/73 sale catalog.