Memoir 13—Nautiloid Shell Morphology

By R. H. Flower, 1964, 79 pp., 23 figs., 6 plates, 1 glossary, 1 index.

The fundamental parts of the nautiloid shell are (1) conch, (2) septa, (3) connecting ring, (4) siphonal deposits, and (5) cameral deposits. It is important to recognize that the septal neck and connecting ring, ordinarily considered the two hard parts of the siphuncle universally developed, are discrete structures. Classification of siphonal deposits by shape separates homologous structures and unites unrelated ones. A better approach in terms of composition, textures, and mode of secretion is not yet possible, but it is evident that some deposits are true parts of the rings; others are derived from the ring, but now distinct from it; still others are distinct from the ring, cenogenetic in the various orders, and secreted within the siphonal strand; and some are possibly secreted as mantle deposits on its surface. Evidence being ambiguous in some instances, the siphonal deposits are treated in terms of their evolution, in terms of the orders or parts of orders in which they develop. New observations on a number of structures are included.