The Gazophylacium of Jacob Petiver, Apothecary in London (died 1715) is a very rare book, as the plates and the catalogues were printed and published at different times between 1695 and 1715. They were collected later and published by Mr. Empson, an officer of the British Museum and a natural son of Sir Hans Sloane, in 1764, in London, with the title, “Jacobi Petiveri Opera, etc., or Gazophylacium, 2 vol. fol.” A small volume in 8vo contains the original sheets published by Petiver between 1695 and 1706. The library of the Museum of Comp. Zool. at Cambridge possesses a copy presented, June 1765 by Emanuel Mendez da Costa, Librarian of the Royal Society, to Thomas Knowlton. The collection of J. Petiver, at least the Lepidoptera, is still preserved in the British Museum, and was seen by me in 1857. Every butterfly is placed between two thin plates of mica, fastened with a small band of paper around the margin, and glued with one flying slip to the pages of a book in quarto, so that every species can be examined above and beneath.