MLA

Wharton, Edith, 1862-1937. Howells, William D.. Box 61, folder 1736. 1902 May 26. https://collections.library.yale.edu/catalog/17111185.

APA, 6th edition

Wharton, Edith, 1862-1937. (["Box 61, folder 1736"])(1902 May 26)[Howells, William D.]. https://collections.library.yale.edu/catalog/17111185.