MLA

Pforzheimer, Walter L. (Walter Lionel), 1914-2003. "In the village store" for St. Nicholas; ink and watercolor on Bristol board. Box 5, folder 51. undated. https://collections.library.yale.edu/catalog/12332341.

APA, 6th edition

Pforzheimer, Walter L. (Walter Lionel), 1914-2003. (["Box 5, folder 51"])(undated)["In the village store" for St. Nicholas; ink and watercolor on Bristol board]. https://collections.library.yale.edu/catalog/12332341.