Diadumenian, AE30, Sinope, Paphlagonien. Dated CY 261 (AD 217). 

M OPEL DIADOYMENIANVS CAES, bare-headed, draped, cuirassed bust right.
C I F SINOPN CCLXI, Serapis standing left, holding sceptre
and raising right hand.

Megaw SIN4.
With permission of cngcoins.com, July 2007.

(The reference refers to Malcolm Megaw's book of the Provincial
Coinage of Diadumenian).