MLA

Miller, Henry, 1891-1980. Xerxes Society. Box 10, folder 128-129. 1910-1912, undated. https://collections.library.yale.edu/catalog/11140790.

APA, 6th edition

Miller, Henry, 1891-1980. (["Box 10, folder 128-129"])(1910-1912, undated)[Xerxes Society]. https://collections.library.yale.edu/catalog/11140790.