Pius, P. C. C. P. (1931). After Forty Years, Encyclical Letter of His Holiness, Pius XI by Divine Providence Pope. New York.
Chicago Style (17th ed.) CitationPius, Pope; Catholic Church. Pope. After Forty Years, Encyclical Letter of His Holiness, Pius XI by Divine Providence Pope. New York, 1931.
MLA (8th ed.) CitationPius, Pope; Catholic Church. Pope. After Forty Years, Encyclical Letter of His Holiness, Pius XI by Divine Providence Pope. New York, 1931.
Warning: These citations may not always be 100% accurate.