MLA

Stieglitz, Alfred, 1864-1946. Letters. Box 67, folder 1492-1493. 1931 Oct. https://collections.library.yale.edu/catalog/2040962.

APA, 6th edition

Stieglitz, Alfred, 1864-1946. (["Box 67, folder 1492-1493"])(1931 Oct)[Letters]. https://collections.library.yale.edu/catalog/2040962.