Severus Alexander, AE17 of Nicaea, Bithynia.

(M AVR CEV ALEXANDROC AV), laureate, draped bust right,
countermark of chimera (?) on neck.
NI-KAIE-WN in three lines within wreath.

SNG Righetti 642; RecGen -.
(I can't find a Howgego ref. for this countermark).

Offered on ebay by highrating_lowprice, March 2012.