This is a die trial, in white metal, of the 1867 without rays reverse used on J418/P490 and others before the addition of the border dentilation.
It is listed under 1866 in error in Pollock and the other reference works. This die is Pollock's reverse B under J573/P650 which was not used by the mint on any 1866 patterns.
A couple of the reverse B dies did get out of the mint and were used to strike various patterns by Joseph Mickley and Sylvester Crosby. For additional information on these, click here.
Only 2 of these die trials are known. One was part of the Lohr collection and the other, illustrated, was part of the materials purchased by the Library Company of Philadelphia from Maxwell Whiteman. It is listed as inventory #7.
The Connecticut State Library piece (inventory #15093), also listed by Pollock and Taxay, was seen by your editor and is a die cap mint error.
Photo courtesy of the Library Company of Philadelphia.