MLA

Stein, Gertrude, 1874-1946. La Motte, Ellen. Box 137, folder 3155. 1946 Jul 28. https://collections.library.yale.edu/catalog/17105792.

APA, 6th edition

Stein, Gertrude, 1874-1946. (["Box 137, folder 3155"])(1946 Jul 28)[La Motte, Ellen]. https://collections.library.yale.edu/catalog/17105792.