MLA

Van Vechten, Carl, 1880-1964. Caldwell, Erskine. Box 339, folder 4332. 1938 March 24. https://collections.library.yale.edu/catalog/2031469.

APA, 6th edition

Van Vechten, Carl, 1880-1964. (["Box 339, folder 4332"])(1938 March 24)[Caldwell, Erskine]. https://collections.library.yale.edu/catalog/2031469.