MLA

Pound, Ezra, 1885-1972. Madrigal: autograph ms.. Box 80, folder 3548. [1910]. https://collections.library.yale.edu/catalog/17430565.

APA, 6th edition

Pound, Ezra, 1885-1972. (["Box 80, folder 3548"])([1910])[Madrigal: autograph ms.]. https://collections.library.yale.edu/catalog/17430565.