MLA

Eliot, George, 1819-1880. Letter. Box 9. 1881 May 27. https://collections.library.yale.edu/catalog/32368881.

APA, 6th edition

Eliot, George, 1819-1880. (["Box 9"])(1881 May 27)[Letter]. https://collections.library.yale.edu/catalog/32368881.