MLA

Van Vechten, Carl, 1880-1964. Nathan, George Jean. Box 369, folder 5213. 1939 April 25. https://collections.library.yale.edu/catalog/2109336.

APA, 6th edition

Van Vechten, Carl, 1880-1964. (["Box 369, folder 5213"])(1939 April 25)[Nathan, George Jean]. https://collections.library.yale.edu/catalog/2109336.