Watch List notes:

L. Caecilius Metellus Diadematus or Delmaticus. AR Denarius, 128 BC. Cr. 262/1 var, (mark of value); B. 38 var. (same). AR. 3.84 g. 18.50 mm. RRR. Extremely rare and apparently unpublished variety, with mark of value X misengraved instead of XVI monogram. A superb example, from masterly engraved dies. Small reverse delamination. Lovely even grey toning. EF. Since its introduction in 211 BC circa, a denarius had been reckoned at ten asses, hence the X on most. Circa 140 BC, for the gradual reduction in the size of bronze denominations, the denarius was retariffed to sixteen asses.
The new mark of value XVI, first appeared in BC 141 on the denarius of L.Julius (Cr. 224/1)  was soon replaced by another mark of value, first appeared on the denarius of L. Antestius Gragulus in BC 136 (Cr. 238/1). This new mark, an X now with a horizontal bar through the centre, is sometimes read as a monogram of XVI. .