Vergl. Physiologie d. niederen Thiere, 1903, p. 441.
For further details see Zittel, Lehrbuch der Palaeontologie, and Felix Bernard, Eléments de Palaeontologie, 1894.
For further details see Sollas, "The Formation of Flints," in The Age of the Earth, 1905, p. 131.
Willey's Zool. Results, pt. ii. 1899, p. 127.
Murbach, Archiv f. Naturg. lx. Bd. i. 1894, p. 217.