The Secretary of the Interior is authorized and directed to prepare a roll of the Indians of the blood of the Otoe and Missouria Tribe whose names appear on the allotment rolls of the tribe approved December 7, 1899, June 1, 1906, and January 17, 1907, and who are living on May 9, 1958, and the descendants of such allottees who are living on May 9, 1958, regardless of whether such allottees are living or deceased. Applications for enrollment shall be filed within six months after May 9, 1958. The determination of the Secretary regarding the eligibility of an applicant for enrollment shall be final and conclusive.