MLA

Stieglitz, Alfred, 1864-1946. Underwood, W. Orison. Box 50, folder 1186. 1911-14. https://collections.library.yale.edu/catalog/17105663.

APA, 6th edition

Stieglitz, Alfred, 1864-1946. (["Box 50, folder 1186"])(1911-14)[Underwood, W. Orison]. https://collections.library.yale.edu/catalog/17105663.