Nautiloceras
Introduction '''''Nautiloceras''''' is an extinct genus from the nautiloid order Nautilida, which includes the living ''Nautilus'' and its close relative ''Allonautilus''. ''Nautiloceras'' is a poorly known genus that probably belongs to the Trigonoceratidae. According to Kummel (1964) ''Nautiloceras'' is a jr synonym for ''Trigonoceras'' which was named by M'Coy in 1948.Different ages are given for the two however, with ''Nautiloceras'' being from the Upper Tournesian, about 352-345 Ma, (Lower Osage) and Trigonoceras somewhat younger, Upper Visean - Lower Serpukhovian, (Upper Meremec - Chester) with the span from about 340 to 322 Ma.Nautiloceras  may have been cyrtconic to loosely gyroconic, coiled without whorls being in contact with one another. Gyroconic forms may have had a subtriangular cross section with a broad concave venter, occupying the outer rim.
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