MLA

Luhan, Mabel Dodge, 1879-1962. Mitchison, Naomi. Box 26, folder 716-717. 1935-36, n.d.. https://collections.library.yale.edu/catalog/17085359.

APA, 6th edition

Luhan, Mabel Dodge, 1879-1962. (["Box 26, folder 716-717"])(1935-36, n.d.)[Mitchison, Naomi]. https://collections.library.yale.edu/catalog/17085359.