MLA

Luhan, Mabel Dodge, 1879-1962. MacKaye, Percy. Box 65, folder 1766. n.d.. https://collections.library.yale.edu/catalog/10268282.

APA, 6th edition

Luhan, Mabel Dodge, 1879-1962. (["Box 65, folder 1766"])(n.d.)[MacKaye, Percy]. https://collections.library.yale.edu/catalog/10268282.