MLA

Stein, Gertrude, 1874-1946. Cone, Claribel. Box 153, folder 3759-3760. n.d.. https://collections.library.yale.edu/catalog/9998171.

APA, 6th edition

Stein, Gertrude, 1874-1946. (["Box 153, folder 3759-3760"])(n.d.)[Cone, Claribel]. https://collections.library.yale.edu/catalog/9998171.