MLA

Murphy, Gerald, 1888-1964. Hemingway, Mary Welsh. Box 4, folder 71. 1965 December 15, undated. https://collections.library.yale.edu/catalog/32308388.

APA, 6th edition

Murphy, Gerald, 1888-1964. (["Box 4, folder 71"])(1965 December 15, undated)[Hemingway, Mary Welsh]. https://collections.library.yale.edu/catalog/32308388.