MLA

Stieglitz, Alfred, 1864-1946. Letters. Box 86, folder 1734-1737. 1931 Mar-May. https://collections.library.yale.edu/catalog/2040174.

APA, 6th edition

Stieglitz, Alfred, 1864-1946. (["Box 86, folder 1734-1737"])(1931 Mar-May)[Letters]. https://collections.library.yale.edu/catalog/2040174.