A city man accused of robbing a Watertown Savings Bank Branch earlier this month has pleaded guilty and will be sentenced next month. Forty four year old Michael Merrifield pleaded guilty Monday to a count of third degree robbery. He admitted to entering the main branch on Clinton St. back on March 3, and handing a teller a note threatening her unless she gave him money. Merrifield then fled the scene with under three thousand dollars before being arrested by city police later that same evening. Merrifield, who has served time for other criminal offenses, faces two and a half to five years in prison when sentenced on April 24.