MLA

Butts, Mary, 1890-1937. Ross Williamson, Hugh. Box 1, folder 36. 1931-34. https://collections.library.yale.edu/catalog/16893663.

APA, 6th edition

Butts, Mary, 1890-1937. (["Box 1, folder 36"])(1931-34)[Ross Williamson, Hugh]. https://collections.library.yale.edu/catalog/16893663.