MLA

Stieglitz, Alfred, 1864-1946. Buehrmann, Elizabeth; Buehrmann, Mary. Box 8, folder 192. 1906-33, n.d.. https://collections.library.yale.edu/catalog/16232718.

APA, 6th edition

Stieglitz, Alfred, 1864-1946. (["Box 8, folder 192"])(1906-33, n.d.)[Buehrmann, Elizabeth; Buehrmann, Mary]. https://collections.library.yale.edu/catalog/16232718.