Hi glorkar,
This is from "British Commonwealth Coins" by J.Remick, S.James, A.Dowle and P.Finn
With Bust A or B:
I) no mm (Calcutta or Bombay)
2) C incuse on shell on reverse near bottom of coin (Calcutta).
3) B incuse in flower on reverse near top of coin. B is upside-down on a few coins. (Bombay).
4) B raised in flower on reverse near top of coin. (Bombay).
5) Dot under date and just above shell. (Bombay).
This site is a great help to find out varieties on B.I. coins,
http://baldwin.co.uk/coins-of-india/VictoriaEmpress/CatVicEmpress_TwoAnnas1.htm