Nautiloceras is an extinct genus from the nautiloid order Nautilida,[1] 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)[2] Nautiloceras is a jr synonym for Trigonoceras which was named by M'Coy in 1948. Different ages are given for the two however,[3] 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 [2] 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.