MLA

Pearson, Norman Holmes, 1909-1975. Cather, Willa. Box 27. 1937. https://collections.library.yale.edu/catalog/33298706.

APA, 6th edition

Pearson, Norman Holmes, 1909-1975. (["Box 27"])(1937)[Cather, Willa]. https://collections.library.yale.edu/catalog/33298706.