MLA

Schletter, Annie, 1858-1944. Haines, Frederick Paul, Sir. Box 1, folder 18. 1890 June. https://collections.library.yale.edu/catalog/17453743.

APA, 6th edition

Schletter, Annie, 1858-1944. (["Box 1, folder 18"])(1890 June)[Haines, Frederick Paul, Sir]. https://collections.library.yale.edu/catalog/17453743.