Cite

[No. 21: Photograph of dead bighorn sheep]

MLA

[No. 21: Photograph of Dead Bighorn Sheep]. 1915. https://collections.library.yale.edu/catalog/11679613.

APA, 6th edition

[No. 21: Photograph of dead bighorn sheep]. (1915). [Photographs, Slides (glass)]. https://collections.library.yale.edu/catalog/11679613.