MLA

Saarinen, Eero, 1910-1961. Additional material. Box 678, folder 121. undated. https://collections.library.yale.edu/catalog/10021526.

APA, 6th edition

Saarinen, Eero, 1910-1961. (["Box 678, folder 121"])(undated)[Additional material]. https://collections.library.yale.edu/catalog/10021526.