MLA

Hartley, Marsden, 1877-1943. Von Freyburg, Carl. Box 12. 1909-1913, undated. https://collections.library.yale.edu/catalog/17188753.

APA, 6th edition

Hartley, Marsden, 1877-1943. (["Box 12"])(1909-1913, undated)[Von Freyburg, Carl]. https://collections.library.yale.edu/catalog/17188753.