Ozarkian and Canadian Cephalopods: Part III: Longicones and Summary
E. O. ULRICH, AUG. F. FOERSTE, A. K. MILLER, A. G. UNKLESBAY, 1944. "Ozarkian and Canadian Cephalopods: Part III: Longicones and Summary", Ozarkian and Canadian Cephalopods: Part III: Longicones and Summary, E. O. Ulrich, Aug. F. Foerste, A. K. Miller, A. G. Unklesbay
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Long slender straight and slightly curved nautiloids are of widespread occurrence in the Early Paleozoic of the United States, Canada, and Newfoundland. They appear in the Lower Ozarkian and are abundant in the Upper Ozarkian and the Upper Canadian. A few species are known from contemporaneous beds in Greenland, northwestern Europe, eastern Asia, and probably Australia and South America.
Externally most of the American forms are similar, though some are smooth and others are annulated. Chiefly on the basis of the figure of the conch, the nature of the surface, the shape of the sutures, and particularly the structure of the siphuncle they have been divided into eleven families: the Stemtonoceratidae (3 species representing 2 genera), the Endocycloceratidae (5 species, 2 genera), the Bassleroceratidae (41 species, 10 genera), the Rudolfoceratidae (8 species, 3 genera), the Orthocerotidae (20 species, 7 genera), the Robsonoceratidae (2 species, 1 genus), the Spyroceratidae (29 species, 3 genera), the Endoceratidae (70 species, 9 genera), the Suecoceratidae (3 species, 1 genus), the Bathmoceratidae (1 species, 1 genus), and the Eothinoceratidae (1 species, 1 genus). All but four of these families are represented in both the Ozarkian and the Canadian, and these four contain only a few aberrant forms.