MLA

Purdy, James, 1914-2009. Rorem, Ned. Box 17, folder 352. n.d.. https://collections.library.yale.edu/catalog/2042578.

APA, 6th edition

Purdy, James, 1914-2009. (["Box 17, folder 352"])(n.d.)[Rorem, Ned]. https://collections.library.yale.edu/catalog/2042578.