MLA

Wilfred, Thomas, 1889-1968. Sketches. Box 12, folder 172-175. Undated. https://collections.library.yale.edu/catalog/10015946.

APA, 6th edition

Wilfred, Thomas, 1889-1968. (["Box 12, folder 172-175"])(Undated)[Sketches]. https://collections.library.yale.edu/catalog/10015946.