MLA

Van Vechten, Carl, 1880-1964. Chávez, Carlos. Box 340, folder 4380. 1937 March 3. https://collections.library.yale.edu/catalog/2031900.

APA, 6th edition

Van Vechten, Carl, 1880-1964. (["Box 340, folder 4380"])(1937 March 3)[Chávez, Carlos]. https://collections.library.yale.edu/catalog/2031900.