For a comparable obsidian and rock crystal group model of two seals, see exhibition catalogue, The Fabergé Menagerie, Baltimore, The Walters Art Museum, Baltimore, 2003, pp. 182-183, no. 115. A related chalcedony model of a penguin also forms part of the Royal Collection, see C. de Guitaut, Fabergé in the Royal Collection, London, pp. 88-89, no. 88 (RCIN 40285).