MLA

Acton, Harold, 1904-1994. Other Letters and Papers. Box 3, folder 212-217. 1931-1941. https://collections.library.yale.edu/catalog/17452764.

APA, 6th edition

Acton, Harold, 1904-1994. (["Box 3, folder 212-217"])(1931-1941)[Other Letters and Papers]. https://collections.library.yale.edu/catalog/17452764.