MLA

Van Vechten, Carl, 1880-1964. Horne, William. Box 353, folder 4766. 1947 July 6. https://collections.library.yale.edu/catalog/2047128.

APA, 6th edition

Van Vechten, Carl, 1880-1964. (["Box 353, folder 4766"])(1947 July 6)[Horne, William]. https://collections.library.yale.edu/catalog/2047128.