MLA

Stein, Leo, 1872-1947. Coubine, Otakar Coubine, Bertha. Box 3, folder 75-77. 1926-49, n.d.. https://collections.library.yale.edu/catalog/17155342.

APA, 6th edition

Stein, Leo, 1872-1947. (["Box 3, folder 75-77"])(1926-49, n.d.)[Coubine, Otakar Coubine, Bertha]. https://collections.library.yale.edu/catalog/17155342.