MLA

Sergeant, Elizabeth Shepley, 1881-1965. Howard, Sidney. Box 14, folder 315. 1918, 1939, n.d.. https://collections.library.yale.edu/catalog/10542964.

APA, 6th edition

Sergeant, Elizabeth Shepley, 1881-1965. (["Box 14, folder 315"])(1918, 1939, n.d.)[Howard, Sidney]. https://collections.library.yale.edu/catalog/10542964.