MLA

Stein, Gertrude, 1874-1946. Marcoussis, Louis. Box 116, folder 2437. 1931, n.d.. https://collections.library.yale.edu/catalog/17105754.

APA, 6th edition

Stein, Gertrude, 1874-1946. (["Box 116, folder 2437"])(1931, n.d.)[Marcoussis, Louis]. https://collections.library.yale.edu/catalog/17105754.