MLA

Van Thal, Herbert, 1904-1983. Blackwell, Basil. Box 1, folder 15. 1955 Oct 13. https://collections.library.yale.edu/catalog/16545919.

APA, 6th edition

Van Thal, Herbert, 1904-1983. (["Box 1, folder 15"])(1955 Oct 13)[Blackwell, Basil]. https://collections.library.yale.edu/catalog/16545919.