This is Sear 2149 Uncertain of Nicaea, DOC IV Uncertain B.2 (Pl. XXXVII, B.2).
It is one of the rare “Christ Chalkites” types, along with S.2148, S.2150 & S.2153.
See below for two more examples of S.2149 posted on Forum Byzantine on (or about) 13/12/2012.
The top (neatly clipped) coin was from Orthodox Coins and the second from a private collection.
Ross G.