MLA

Williams, William Carlos, 1883-1963. Johns, Richard. Box 9, folder 330. 1932-1939, undated. https://collections.library.yale.edu/catalog/17049495.

APA, 6th edition

Williams, William Carlos, 1883-1963. (["Box 9, folder 330"])(1932-1939, undated)[Johns, Richard]. https://collections.library.yale.edu/catalog/17049495.