MLA

Stieglitz, Alfred, 1864-1946. Letters. Box 84, folder 1707-1708. 1928 May. https://collections.library.yale.edu/catalog/2039730.

APA, 6th edition

Stieglitz, Alfred, 1864-1946. (["Box 84, folder 1707-1708"])(1928 May)[Letters]. https://collections.library.yale.edu/catalog/2039730.