MLA

Van Vechten, Carl, 1880-1964. Werfel, Franz. Box 382, folder 5701. 1940 December 14. https://collections.library.yale.edu/catalog/10636228.

APA, 6th edition

Van Vechten, Carl, 1880-1964. (["Box 382, folder 5701"])(1940 December 14)[Werfel, Franz]. https://collections.library.yale.edu/catalog/10636228.