Butterfield Bank plunged 7 cents (6.54 percent) on the Bermuda Stock Exchange yesterday, with 29,200 shares trading, to close at $1.Butterfield Preferred traded 518 shares with no change in share price to close at $1,230.Overall, the BSX closed at 970.63, down 33.17 points (3.30 percent) with 29,200 shares trading worth $29,768 and 518 US shares trading worth US$639,928.22