MLA

Henri, Robert, 1865-1929. Correspondence. Box 12, folder 315. 1890 Aug. https://collections.library.yale.edu/catalog/17029582.

APA, 6th edition

Henri, Robert, 1865-1929. (["Box 12, folder 315"])(1890 Aug)[Correspondence]. https://collections.library.yale.edu/catalog/17029582.