MLA

Schletter, Annie, 1858-1944. Braithwaite, Lilian. Box 1, folder 4. n.y. Aug 11. https://collections.library.yale.edu/catalog/17453737.

APA, 6th edition

Schletter, Annie, 1858-1944. (["Box 1, folder 4"])(n.y. Aug 11)[Braithwaite, Lilian]. https://collections.library.yale.edu/catalog/17453737.