MLA

Simpson, Randolph Linsly, 1927-1992. Keystone View Company, Meadville, PA; New York, NY; Chicago, IL; London, ENG. "50 - 13365. America's Most Notable Gathering of Military Heroes -- Left to Right: Jacques (Belgium), Diaz (Italy), Coolidge, Foche (France), Pershing, end, Beatty (England) at his right." Stereograph, grey card. Box 13, folder 629. circa 1920. https://collections.library.yale.edu/catalog/16172756.

APA, 6th edition

Simpson, Randolph Linsly, 1927-1992. (["Box 13, folder 629"])(circa 1920)[Keystone View Company, Meadville, PA; New York, NY; Chicago, IL; London, ENG. "50 - 13365. America's Most Notable Gathering of Military Heroes -- Left to Right: Jacques (Belgium), Diaz (Italy), Coolidge, Foche (France), Pershing, end, Beatty (England) at his right." Stereograph, grey card]. https://collections.library.yale.edu/catalog/16172756.