MLA

Brooks, Cleanth, 1906-1994. The Bollingen Prize in Poetry. Box 87, folder 1783. 1949-50. https://collections.library.yale.edu/catalog/17103611.

APA, 6th edition

Brooks, Cleanth, 1906-1994. (["Box 87, folder 1783"])(1949-50)[The Bollingen Prize in Poetry]. https://collections.library.yale.edu/catalog/17103611.