The period of trust on lands allotted to Indians of the Klamath River Reservation, California, which expired July 31, 1919, and the legal title to which is still in the United States, is reimposed and extended for a period of twenty-five years from July 31, 1919: Provided, That further extension of the period of trust may be made by the President, in his discretion, as provided by section 348 and section 391 of this title.