20セント硬貨 (アメリカ合衆国)
↑ Taxay, pp. 262–263.
↑ Hammer, p. 167.
1 2 Breen, p. 334.
↑ Yeoman, p. 163.
書籍
Breen, Walter (1988). Walter Breen's Complete Encyclopedia of U.S. and Colonial Coins. New York: Doubleday. ISBN 978-0-385-14207-6
Bureau of the Mint (1904). Laws of the United States Relating to the Coinage. Washington, DC: United States Government Printing Office. https://books.google.co.jp/books?id=rmtAAAAAYAAJ&redir_esc=y&hl=ja
Lange, David W. (2006). History of the United States Mint and its Coinage. Atlanta, GA: Whitman Publishing. ISBN 978-0-7948-1972-9
Taxay, Don (1983). The U.S. Mint and Coinage (reprint of 1966 ed.).