MLA

Eliot, George, 1819-1880. Letter. Box 11. [1885 Mar?]. https://collections.library.yale.edu/catalog/32365699.

APA, 6th edition

Eliot, George, 1819-1880. (["Box 11"])([1885 Mar?])[Letter]. https://collections.library.yale.edu/catalog/32365699.