Watch List notes:

Potosi, Bolivia, cob 8 reales, 1651 O, with pentagonal crowned-1605 (Mastalir P05) countermark on cross, very rare, Mastalir Plate. S-P35; KM-19b; Cal-1489. 17.87 grams. A thin but very well-detailed example (contrastingly toned) with full shield and cross, full P-O and 8-O, and clear 51 of date, but most important part is the full pentagonal countermark near edge on cross side with 1605 date below crown, one of only two known with visible date on host coin and three known overall, a countermark that has also been seen on silver pieces from the Atocha (1622). Pedigreed to the Roberto Mastalir Collection of Countermarked Potosi Cobs, Plate Coin (page 194 in Part A and page 390 in Part B) in his book The Great Transition at the Potosi Mint, 1649-1653, The 1649-1652 Crowned Shield Coinage and the Countermarks of 1652 (2021), with original Herman Moro certificate. From: Capitana, sunk in 1654 off Chanduy, Ecuador
($500-750)