MLA

Luhan, Mabel Dodge, 1879-1962. Pelton, Agnes. Box 28, folder 808. 1921-38, n.d.. https://collections.library.yale.edu/catalog/17085363.

APA, 6th edition

Luhan, Mabel Dodge, 1879-1962. (["Box 28, folder 808"])(1921-38, n.d.)[Pelton, Agnes]. https://collections.library.yale.edu/catalog/17085363.