A fine complete typical adult internal mould showing the blunt ribbing almost to the end, The body chamber ocuppies 2/3 whorl and has a terminal constriction and complete peristome. It is partly erode on one side. It shows the first morphological change in the Cardioceratidae from the sperical coiling of Spheeroceras and Cranocephalites borealis, to more evolute round whorled shells seen in CAR 3A and CAR 4A. Blunt ribbing is retained on the body chambers but the ribbing on the inner whorls was changed by protogenesis (the first appearance of new characters in the early stages of ontogeny) becoming progressively more fine, dense and sharp. From Jameson Land, E Greenland.
Size: 62 mm
Size: 62 mm