20セント硬貨 (アメリカ合衆国)
New York: Sanford J. Durst Numismatic Publications. ISBN 978-0-915262-68-7
Van Allen, Leroy C.; Mallis, A. George (1991). Comprehensive Catalog and Encyclopedia of Morgan & Peace Dollars. Virginia Beach, VA: DLRC Press. ISBN 978-1-880731-11-6
Vermeule, Cornelius (1971). Numismatic Art in America. Cambridge, MA: The Belknap Press of Harvard University Press. ISBN 978-0-674-62840-3
Yeoman, R.S. (2013). A Guide Book of United States Coins (The Official Red Book) (67th ed.). Atlanta, GA: Whitman Publishing. ISBN 978-0-7948-4180-5
その他の情報源
Benvenuto, Tom (August 2003). “Not quite a quarter”. Coins (Iola, WI: Krause Publications, Inc.