MLA

Van Vechten, Carl, 1880-1964. Guillén, Nicolás. Box 224. 1949 March 23. https://collections.library.yale.edu/catalog/2023320.

APA, 6th edition

Van Vechten, Carl, 1880-1964. (["Box 224"])(1949 March 23)[Guillén, Nicolás]. https://collections.library.yale.edu/catalog/2023320.