MLA

Van Vechten, Carl, 1880-1964. Pemberton, Margaret McCoy. Box 385, folder 5791. 1937 May 30. https://collections.library.yale.edu/catalog/10000624.

APA, 6th edition

Van Vechten, Carl, 1880-1964. (["Box 385, folder 5791"])(1937 May 30)[Pemberton, Margaret McCoy]. https://collections.library.yale.edu/catalog/10000624.