MLA

Williams, William Carlos, 1883-1963. Leippert, James George. Box 12, folder 386. 1932, undated. https://collections.library.yale.edu/catalog/17049498.

APA, 6th edition

Williams, William Carlos, 1883-1963. (["Box 12, folder 386"])(1932, undated)[Leippert, James George]. https://collections.library.yale.edu/catalog/17049498.