MLA

Serge, Victor, 1890-1947. Fry, Varian. Box 1, folder 31. 1942. https://collections.library.yale.edu/catalog/16495426.

APA, 6th edition

Serge, Victor, 1890-1947. (["Box 1, folder 31"])(1942)[Fry, Varian]. https://collections.library.yale.edu/catalog/16495426.