Silver denarius, 18mm, 4.01gm, issued 148 BC. Rome mint.
Obv: LIBO, Helmeted head of Roma right, X below chin.
Rev: Q MARC (ROMA in ex.), Dioscuri galloping right.
This issues marks a change in the design of the denarius. The X value mark is moved from behind the head of Roma, to under the chin, and is often replaced by the moneyer's name.