MLA

Mann, Thomas, 1875-1955. Auerbach, Erich. Box 13, folder 220. 1949-51. https://collections.library.yale.edu/catalog/17268857.

APA, 6th edition

Mann, Thomas, 1875-1955. (["Box 13, folder 220"])(1949-51)[Auerbach, Erich]. https://collections.library.yale.edu/catalog/17268857.