MLA

Van Vechten, Carl, 1880-1964. Macpherson, Kenneth. Box 363, folder 5030. 1938 December 21. https://collections.library.yale.edu/catalog/2065527.

APA, 6th edition

Van Vechten, Carl, 1880-1964. (["Box 363, folder 5030"])(1938 December 21)[Macpherson, Kenneth]. https://collections.library.yale.edu/catalog/2065527.