MLA

Matthiessen, F. O. (Francis Otto), 1902-1950. Howe, Irving. Box 2. 1948 October. https://collections.library.yale.edu/catalog/32239655.

APA, 6th edition

Matthiessen, F. O. (Francis Otto), 1902-1950. (["Box 2"])(1948 October)[Howe, Irving]. https://collections.library.yale.edu/catalog/32239655.