MLA

Lewis, Sinclair, 1885-1951. Van Vechten, Carl. Box 54, folder 762-763. 1938 January 5. https://collections.library.yale.edu/catalog/10599430.

APA, 6th edition

Lewis, Sinclair, 1885-1951. (["Box 54, folder 762-763"])(1938 January 5)[Van Vechten, Carl]. https://collections.library.yale.edu/catalog/10599430.