MLA

Van Vechten, Carl, 1880-1964. Williams, Burton. Box 109, folder 1996. 1961 April 4. https://collections.library.yale.edu/catalog/2028752.

APA, 6th edition

Van Vechten, Carl, 1880-1964. (["Box 109, folder 1996"])(1961 April 4)[Williams, Burton]. https://collections.library.yale.edu/catalog/2028752.