MLA

Dreier, Katherine S. (Katherine Sophie), 1877-1952. Invitation. Box 90, folder 2329. n.d.. https://collections.library.yale.edu/catalog/2014461.

APA, 6th edition

Dreier, Katherine S. (Katherine Sophie), 1877-1952. (["Box 90, folder 2329"])(n.d.)[Invitation]. https://collections.library.yale.edu/catalog/2014461.