MLA

Pound, Ezra, 1885-1972. Unidentified musical scores. Box 46, folder 1012-20. n.d.. https://collections.library.yale.edu/catalog/2018539.

APA, 6th edition

Pound, Ezra, 1885-1972. (["Box 46, folder 1012-20"])(n.d.)[Unidentified musical scores]. https://collections.library.yale.edu/catalog/2018539.