United States. Department of the Treasury. "Bill Tender, December 15, 1967, Release Number f-1107," in United States. Department of the Treasury. "Volume 160," Press Releases of the United States Department of the Treasury (December 1, 1967 - February 29, 1968) : 70-72. https://fraser.stlouisfed.org/title/6111/item/587003/toc/540912 , accessed on July 9, 2024.