MLA

Williams, William Carlos, 1883-1963. McDowell, Obolensky Inc.. Box 14, folder 438. 1960. https://collections.library.yale.edu/catalog/17049509.

APA, 6th edition

Williams, William Carlos, 1883-1963. (["Box 14, folder 438"])(1960)[McDowell, Obolensky Inc.]. https://collections.library.yale.edu/catalog/17049509.