MLA

Eliot, George, 1819-1880. Letter. Box 9. [1885?] Mar 9. https://collections.library.yale.edu/catalog/32343965.

APA, 6th edition

Eliot, George, 1819-1880. (["Box 9"])([1885?] Mar 9)[Letter]. https://collections.library.yale.edu/catalog/32343965.