A nice coin!
The
bust type is not unusual, however. Probably just
not in RIC because
Cohen 903 wrongly includes it under "draped,
cuirassed", and the RIC authors didn't bother to check the BM
collection.
BM 286-288 has three specimens like yours. A
hoard we
had several years ago contained 16
denarii with this
rev. type, five of them with the same draped
bust as your coin.
BMC, up to 238 AD, is much more reliable for such details than the first editions of RIC for the period! Seaby's
Roman Silver Coins is also excellent, and of course takes account of
BMC; your coin is
RSC 903a.