MLA

Dreier, Katherine S. (Katherine Sophie), 1877-1952. Feininger, Lyonel. Box 13, folder 355. n.d.. https://collections.library.yale.edu/catalog/16694415.

APA, 6th edition

Dreier, Katherine S. (Katherine Sophie), 1877-1952. (["Box 13, folder 355"])(n.d.)[Feininger, Lyonel]. https://collections.library.yale.edu/catalog/16694415.