MLA

Williams, William Carlos, 1883-1963. Herbst, Josephine. Box 8, folder 277. 1950-1961, undated. https://collections.library.yale.edu/catalog/17049486.

APA, 6th edition

Williams, William Carlos, 1883-1963. (["Box 8, folder 277"])(1950-1961, undated)[Herbst, Josephine]. https://collections.library.yale.edu/catalog/17049486.