MLA

Bird, William, 1888-1963. Canto XII. Box 2, folder 80. n.d.. https://collections.library.yale.edu/catalog/16164970.

APA, 6th edition

Bird, William, 1888-1963. (["Box 2, folder 80"])(n.d.)[Canto XII]. https://collections.library.yale.edu/catalog/16164970.