MLA

Stieglitz, Alfred, 1864-1946. Joseph Obermeyer. Box 130, folder 2521. ca. 1917. https://collections.library.yale.edu/catalog/2002560.

APA, 6th edition

Stieglitz, Alfred, 1864-1946. (["Box 130, folder 2521"])(ca. 1917)[Joseph Obermeyer]. https://collections.library.yale.edu/catalog/2002560.