MLA

Serge, Victor, 1890-1947. Werth, Leon. Box 2, folder 87. 1939-41. https://collections.library.yale.edu/catalog/16495442.

APA, 6th edition

Serge, Victor, 1890-1947. (["Box 2, folder 87"])(1939-41)[Werth, Leon]. https://collections.library.yale.edu/catalog/16495442.