MLA

Hartley, Marsden, 1877-1943. Letters. Box 9. 1933-1943. https://collections.library.yale.edu/catalog/16827254.

APA, 6th edition

Hartley, Marsden, 1877-1943. (["Box 9"])(1933-1943)[Letters]. https://collections.library.yale.edu/catalog/16827254.