2 of his scientific books, pamphlets, notes and correspondence to the Boston Society of Natural History. In 1941, the Society donated the Bailey Collection to the Farlow Herbarium of Harvard University, where it currently resides. Since 1976, I have worked at the Farlow Herbarium restoring those portions of the Bailey Collection which contained diatoms to a condition that would make them useful to contemporary taxonomists and historians of science. As the initial step in this restoration, I prepared a bibliography of Bailey's scientific contributions (Edgar, 1977). In promoting further this restoration this present work defines the present extent of the collection and indexes the taxa, geographical locations and persons associated with the diatom portions of it. The Bailey Collection: 1857-1941 The general contents of the Bailey bequest to the Boston Society of Natural History are clear, but an itemized account of most parts of the collection has not been found and doubtfully was one made. Consequently, the extent of the diatom contents of the original collection can be approximated only. The bequest circumscribes initially the collection (Proc. Boston Soc. nat. Hist. 6:179-181. 1857.): Bequest of Prof. J.W. Bailey. First. A microscopic collection, contained in cases resembling books, together with said cases, and the index volumes thereunto belonging; the whole bearing for titles, "Microscopic Collections." Second. The whole of my collection of Algae, or Seaweeds, as contained in a set of portfolios, together with said portfolios.