United States. Department of the Treasury. "Bill Tender, September 25, 1967, Release Number f-1040," in United States. Department of the Treasury. "Volume 159," Press Releases of the United States Department of the Treasury (September 1, 1967 - November 29, 1967) : 203-204. https://fraser.stlouisfed.org/title/6111/item/587002/toc/540657 , accessed on May 4, 2024.