MLA

Richards, David Alan, 1945-. Nicholson, William: Rudyard Kipling. Box 39. undated. https://collections.library.yale.edu/catalog/2022946.

APA, 6th edition

Richards, David Alan, 1945-. (["Box 39"])(undated)[Nicholson, William: Rudyard Kipling]. https://collections.library.yale.edu/catalog/2022946.