These are principally letters to Charles Edward Sayle on musical programs and to Thomas Roscoe Rede Stebbing about the Linnean Society, the Royal Society, and the publication of Charles Darwin's papers. There is also a letter of Charles Darwin to Stebbings and several letters of Francis Darwin to other persons. In addition, there are several letters to William Bowman (as well as from Theodor Wilhelm Engelmann to Bowman), and one from Raphael Meldola.

This collection includes correspondence on natural history and evolution, and especially on his collection and study of shells from Japan and the Pacific islands. Principal correspondents include Louis Agassiz, Charles Robert Darwin, Sir William Henry Flower, Alpheus Hyatt, George Newbold Lawrence, George J. Romanes, Alfred R. Wallace, and the Linnean Society of London.