MLA

Schletter, Annie, 1858-1944. Clifford, Elizabeth, Lady. Box 1, folder 8. 1916 Aug 25. https://collections.library.yale.edu/catalog/17453740.

APA, 6th edition

Schletter, Annie, 1858-1944. (["Box 1, folder 8"])(1916 Aug 25)[Clifford, Elizabeth, Lady]. https://collections.library.yale.edu/catalog/17453740.