MLA

Huntington, Ellsworth, 1876-1947. E. Box 1, folder 6. 1947, undated. https://collections.library.yale.edu/catalog/32507054.

APA, 6th edition

Huntington, Ellsworth, 1876-1947. (["Box 1, folder 6"])(1947, undated)[E]. https://collections.library.yale.edu/catalog/32507054.