MLA

Williams, Oscar, 1900-1964. Williams, Oscar. Box 1 | Folder 31. undated. https://collections.library.yale.edu/catalog/17104200.

APA, 6th edition

Williams, Oscar, 1900-1964. (["Box 1 | Folder 31"])(undated)[Williams, Oscar]. https://collections.library.yale.edu/catalog/17104200.