MLA

Matthiessen, F. O. (Francis Otto), 1902-1950. VanDoren, Mark. Box 4. 1949 March 23. https://collections.library.yale.edu/catalog/32240004.

APA, 6th edition

Matthiessen, F. O. (Francis Otto), 1902-1950. (["Box 4"])(1949 March 23)[VanDoren, Mark]. https://collections.library.yale.edu/catalog/32240004.