Knight Capital ( NITE) plunged more than 12% after an analyst with Sandler O'Neill said its "core" trade execution business showed signs of stalling in the quarter despite a reported 12% gain in fourth-quarter profits. Earnings came to 33 cents a share, excluding items, which beats the consensus by a penny, but the analyst noted that only 12 cents of the total derived from the firm's market-making division. Shares were losing $2.67 to $18.79. Nasdaq Stock Market ( NDAQ) sank after the London Stock Exchange, in further defense against Nasdaq's $5.2 billion hostile bid for the British exchange, said it will boost its share buyback program by as much as $491 million. Shares were falling 99 cents, or 2.8%, to $34.46. Sovereign Bancorp ( SOV) fell after it swung to a loss in the fourth quarter and sharply narrowed its full-year gains. The Philadelphia-based bank lost $129.4 million for the quarter, or 28 cents a share, compared with profits of $165.5 million, or 42 cents a share, a year ago. Full-year earnings came to $136.9 million, or 30 cents a share, compared with last year's $676.2 million, or $1.77 a share. Shares were down 65 cents, or 2.6%, to $24.36. North Bay Bancorp ( NBAN) jumped after the Napa, Calif.-based regional bank agreed to be bought by Umpqua Holdings ( UMPQ) for a total stock-based value of about $156 million. North Bay shares were adding $4.18, or 13.9%, to $34.18. Portland, Ore.-based Umpqua was down 25 cents, or 0.9%, to $28.52.