MLA

Butts, Mary, 1890-1937. Atkin, Gabriel. Box 1, folder 1. 1928, n.d.. https://collections.library.yale.edu/catalog/16893629.

APA, 6th edition

Butts, Mary, 1890-1937. (["Box 1, folder 1"])(1928, n.d.)[Atkin, Gabriel]. https://collections.library.yale.edu/catalog/16893629.