Other
MLA
McKay, Claude, 1890-1948. Other. Box 18, folder 556. n.d.. https://collections.library.yale.edu/catalog/10171943.
APA, 6th edition
McKay, Claude, 1890-1948. (["Box 18, folder 556"])(n.d.)[Other]. https://collections.library.yale.edu/catalog/10171943.