A beautiful piece. A rare coin in this condition.
A variant of reverse punctuation not described in Iger.
Obverse: royal bust in crown, and armor, with tubular orifice seen from above, to the right, in the rim legend:
SIGI-3-D-G-REX-PO-M-D-L-;
Reverse: denomination III, below it the coats of arms of the Eagle of the Crown, the Sheaf of the Vasa dynasty and the Pose of the Grand Duchy of Lithuania, below it the legend in three lines:
GROS-ARG-/TRIP-REG-/POLONI:, below it the coat of arms of the Levart in a shield, between the initials of the Great Crown Treasurer Jan Firlej - I-F; in the left field the mint mark "mint hooks" of Teodor Busch, in the right field the abbreviation of the date 91;
