MLA

Luhan, Mabel Dodge, 1879-1962. Dudley, Lotus. Box 10, folder 274. 1919, n.d.. https://collections.library.yale.edu/catalog/17085353.

APA, 6th edition

Luhan, Mabel Dodge, 1879-1962. (["Box 10, folder 274"])(1919, n.d.)[Dudley, Lotus]. https://collections.library.yale.edu/catalog/17085353.