It seems clear from the
legend that the
obverse, shown as
rev. above, must be
Marcus Aurelius. By 161 when he became
Augustus Marcus was already wearing a substantial beard, but I suppose it's possible that a short beard, at least, is concealed by the wear on this specimen.
The
portrait on the
rev., shown as
obv. above, doesn't look like
Antoninus Pius; more likely
Lucius Verus. The
rev. legend would probably have named the emperor and the
mint, but is unfortunately worn away! Curiously the two dies are of different sizes: larger for
Verus, smaller for
Marcus.
Searching
RPC online for
rev. type "
Lucius Verus bust" brings three hits:
10851
Hadrianopolis,
Thrace, AE 22, 4.90g, both emperors laureate not bare-headed, and
Marcus has a slightly different
obv. legend; no picture
3517 Callatis,
Thrace, AE 23, 8.54g, both emperors again laureate not bare-headed, and
Marcus has a slightly different
obv. legend8664
Nicomedia,
Bithynia, AE 26, 9.56g,
Sear 1703 =
BMC 23, both emperors bare-headed, and
Marcus has the same
legend as on Joe's coin.
The first two coins are too small, and vary slightly in
bust type and
obv. legend. The third seems to be a possibility, though Joe's coin would be a larger and heavier variant of the ones known so far.
I will send the picture to Volker Heuchert (
RPC), in the
hope that he can solve the problem!
EDIT: I see
Lucius is apparently laureate not bare-headed on Joe's coin, which differentiates it from the known
Nicomedia specimens.