MLA

Williams, William Carlos, 1883-1963. The Symposium. Box 22, folder 707. 1931-1932. https://collections.library.yale.edu/catalog/17049551.

APA, 6th edition

Williams, William Carlos, 1883-1963. (["Box 22, folder 707"])(1931-1932)[The Symposium]. https://collections.library.yale.edu/catalog/17049551.