25 U.S.C. § 113

At the discretion of the President all disbursements of moneys, whether for annuities or otherwise, to fulfill treaty stipulations with individual Indians or Indian tribes, shall be made in person by the superintendents of Indian affairs, where superintendencies exist, to all Indians or tribes within the limits of their respective superintendencies, in the presence of the local agents and interpreters, who shall witness the same, under such regulations as the Secretary of the Interior may direct.