MLA

Sterne, Maurice, 1878-1957. Mabel Dodge Luhan sketches. Box 23, folder 405. undated. https://collections.library.yale.edu/catalog/2008211.

APA, 6th edition

Sterne, Maurice, 1878-1957. (["Box 23, folder 405"])(undated)[Mabel Dodge Luhan sketches]. https://collections.library.yale.edu/catalog/2008211.