Further remarks on the post-embryonic Hypophylloceras shell

DGF Birkelund, T. & Hansen, H. J.: Further remarks on the post-embryonic Hypophylloceras shell. Bull. geol. Soc. Denmark, Vol. 24, pp. 87-92. Copenhagen, November 19th., 1975. In the light of new studies on the ultrastructures of Dactylioceratidae by M. K. Howarth, a revised model of the post-embryonic shell layers of Hypophylloceras is suggested. The shell consists of an extremely thin outer prismatic layer, a very thin nacreous layer and a relatively thick inner prismatic layer. The outer prismatic layer and the nacreous layer are ribbed distal of third whorl, while the inner side of the inner prismatic layer is smooth. Between the dorsal part of the inner prismatic layer and the preceding whorl cavities occur in the rib intervals. The thickness of the Hypophylloceras shell is about two thirds that of a lytoceratid shell (Saghalinites).

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