Series IV. Natural History includes notebooks of Morse’s boyhood shell cabinet, school essays, lecture notes from Harvard College, illustrations produced for conchologist William G. Binney, extensive notes and sketches relating to mollusca, and research for a proposed textbook entitled Zoology of New England. Included are secondary research materials collected by Morse and filled with his notes. Of interest is a memorandum dated January 14, 1871, in which Morse states his disagreement with Agassiz on the classification of brachiopoda and Darwinian evolutionary theory.