MLA

Van Vechten, Carl, 1880-1964. Hopwood, Avery. Box 56, folder 798-799. 1915-1963, undated. https://collections.library.yale.edu/catalog/32258508.

APA, 6th edition

Van Vechten, Carl, 1880-1964. (["Box 56, folder 798-799"])(1915-1963, undated)[Hopwood, Avery]. https://collections.library.yale.edu/catalog/32258508.