MLA

Marsh, Othniel Charles, 1831-1899. Galton, Lady Douglas. Box 12, folder 492A. 1899. https://collections.library.yale.edu/catalog/32557729.

APA, 6th edition

Marsh, Othniel Charles, 1831-1899. (["Box 12, folder 492A"])(1899)[Galton, Lady Douglas]. https://collections.library.yale.edu/catalog/32557729.