The great Horace Walpole collector Wilmarth Sheldon Lewis described Seymour de Ricci as "the most learned bibliophile of the day" (Collector's Progress, 1951) In his apartment in the rue Boissière in Paris, de Ricci assembled what the bookseller A. S. W. Rosenbach called "the finest private collection of catalogues in the world." In addition to some thirty thousand catalogues from auctions, booksellers, libraries, and exhibitions, chronologically arranged, de Ricci had millions of cards recording the provenance of books and manuscripts. Much of this information he also carried in his head. The rare-book dealer Maurice L. Ettinghausen recalled a meeting with de Ricci at the London house of the collector Henry Yates Thompson at which, after glancing at the binding of a Greek incunabulum, de Ricci recited "not only the eighteenth- and nineteenth-century auction sales in England in which it had figured, but also the prices it had...