MLA

Williams, William Carlos, 1883-1963. Harper's Bazaar. Box 7, folder 261. 1941-1950. https://collections.library.yale.edu/catalog/17049483.

APA, 6th edition

Williams, William Carlos, 1883-1963. (["Box 7, folder 261"])(1941-1950)[Harper's Bazaar]. https://collections.library.yale.edu/catalog/17049483.