MLA

Dreier, Katherine S. (Katherine Sophie), 1877-1952. Chagall, Marc. Box 8, folder 209. 1926. https://collections.library.yale.edu/catalog/16694406.

APA, 6th edition

Dreier, Katherine S. (Katherine Sophie), 1877-1952. (["Box 8, folder 209"])(1926)[Chagall, Marc]. https://collections.library.yale.edu/catalog/16694406.