MLA

Fitzgerald, Robert, 1910-1985. Flores, Angel. Box 12, folder 467. 1956 Aug 20. https://collections.library.yale.edu/catalog/17427377.

APA, 6th edition

Fitzgerald, Robert, 1910-1985. (["Box 12, folder 467"])(1956 Aug 20)[Flores, Angel]. https://collections.library.yale.edu/catalog/17427377.