Code of Federal Regulations Title 25. Indians § 25.11.603 Invalid or prohibited marriages

(1) A marriage entered into prior to the dissolution of an earlier marriage of one of the parties;

(2) A marriage between an ancestor and a descendant, or between a brother and a sister, whether the relationship is by the half or the whole blood;

(3) A marriage between an aunt and a nephew or between an uncle and a niece, whether the relationship is by the half or the whole blood, except as to marriages permitted by established tribal custom;

(4) A marriage prohibited by custom and usage of the tribe.