Note 403 — Chapter XII
Reading edition
The Belemnitic shell presents the same arrangement of its constituent layers as the Pearl-mussel, Pinna, and other Aviculidæ, viz. the outer layer is prismatic-cellular, the inner nacreous: the first is formed by the free margin of the mantle, the second by the visceral ("peritoneal") part of the mantle.—Mr. Woodward.