MLA

Dreier, Katherine S. (Katherine Sophie), 1877-1952. Feininger, Lyonel. Box 102, folder 2509-2510. 1943-50, n.d.. https://collections.library.yale.edu/catalog/16694458.

APA, 6th edition

Dreier, Katherine S. (Katherine Sophie), 1877-1952. (["Box 102, folder 2509-2510"])(1943-50, n.d.)[Feininger, Lyonel]. https://collections.library.yale.edu/catalog/16694458.