MLA

Schwartz, Delmore, 1913-1966. "Morning Bells". Box 3, folder 200. 1938-1958. https://collections.library.yale.edu/catalog/17405244.

APA, 6th edition

Schwartz, Delmore, 1913-1966. (["Box 3, folder 200"])(1938-1958)["Morning Bells"]. https://collections.library.yale.edu/catalog/17405244.