MLA

Williams, William Carlos, 1883-1963. Mallan, Lloyd. Box 14, folder 422. 1941-1942. https://collections.library.yale.edu/catalog/17049504.

APA, 6th edition

Williams, William Carlos, 1883-1963. (["Box 14, folder 422"])(1941-1942)[Mallan, Lloyd]. https://collections.library.yale.edu/catalog/17049504.