MLA

Butts, Mary, 1890-1937. Pryce-Jones, Alan. Box 1, folder 34. n.d.. https://collections.library.yale.edu/catalog/16893661.

APA, 6th edition

Butts, Mary, 1890-1937. (["Box 1, folder 34"])(n.d.)[Pryce-Jones, Alan]. https://collections.library.yale.edu/catalog/16893661.