MLA

McKay, Claude, 1890-1948. Card. Box 9, folder 304. n.d.. https://collections.library.yale.edu/catalog/10034125.

APA, 6th edition

McKay, Claude, 1890-1948. (["Box 9, folder 304"])(n.d.)[Card]. https://collections.library.yale.edu/catalog/10034125.