MLA

Gascoyne, David, 1916-2001. "A Portfolio of New Poems". Box 20, folder 399. 1948. https://collections.library.yale.edu/catalog/2055539.

APA, 6th edition

Gascoyne, David, 1916-2001. (["Box 20, folder 399"])(1948)["A Portfolio of New Poems"]. https://collections.library.yale.edu/catalog/2055539.