X0306 4 2013-12-27 0 0001084554 LIGHTBRIDGE Corp ltbr 0001044321 MARXE AUSTIN W & GREENHOUSE DAVID M C/O SPECIAL SITUATIONS FUNDS 527 MADISON AVENUE, SUITE 2600 NEW YORK NY 10022 0 0 1 0 Common Stock 2013-12-27 4 S 0 16613 1.5741 D 1844142 I By Limited Partnerships Common Stock 2013-12-30 4 S 0 19607 1.57 D 1824535 I By Limited Partnerships This is an average price This is a joint filing by Austin W. Marxe (Marxe) and David M. Greenhouse (Greenhouse). They share voting and investment control over all securities owned by Special Situations Fund III QP, L.P. (QP), Special Situations Cayman Fund, L.P. (Cayman) and Special Situations Private Equity Fund, L.P. (PE). 1,071,110 shares of Common Stock are held by QP, 358,941 shares of Common Stock are held by Cayman, 394,484 shares of Common Stock are held by PE. The interest of Marxe and Greenhouse in the shares of Common Stock owned by QP, Cayman and PE is limited to the extent of his pecuniary interest. David Greenhouse 2013-12-31 Austin Marxe 2013-12-31