MLA

Schwartz, Delmore, 1913-1966. "Cupid and Psyche". Box 3, folder 159. undated. https://collections.library.yale.edu/catalog/17405215.

APA, 6th edition

Schwartz, Delmore, 1913-1966. (["Box 3, folder 159"])(undated)["Cupid and Psyche"]. https://collections.library.yale.edu/catalog/17405215.