MLA

Nicolson, Harold, 1886-1968. Lascelles, Alan, Sir. Box 17. circa 1950s. https://collections.library.yale.edu/catalog/16603670.

APA, 6th edition

Nicolson, Harold, 1886-1968. (["Box 17"])(circa 1950s)[Lascelles, Alan, Sir]. https://collections.library.yale.edu/catalog/16603670.