MLA

Simpson, Kenneth F. (Kenneth Farrand), 1895-1941. Family. Box 36, folder 42. 1936-1939, undated. https://collections.library.yale.edu/catalog/10021436.

APA, 6th edition

Simpson, Kenneth F. (Kenneth Farrand), 1895-1941. (["Box 36, folder 42"])(1936-1939, undated)[Family]. https://collections.library.yale.edu/catalog/10021436.