MLA

Eliot, George, 1819-1880. Letter. Box 9. [1881] Mar 4. https://collections.library.yale.edu/catalog/32368873.

APA, 6th edition

Eliot, George, 1819-1880. (["Box 9"])([1881] Mar 4)[Letter]. https://collections.library.yale.edu/catalog/32368873.