Lituites is an extinct nautiloid genus from the Middle Ordovician and type for the Lituitidae that in some more recent taxonomies has been classified with the orthocerids and listed under the order Lituitida. Fossils have been found in New York, Argentina, Norway, Sweden, Estonia, and China.
The Ellesmerocerida is an order of primitive cephalopods belonging to the subclass Nautiloidea with a widespread distribution that lived during the Late Cambrian and Ordovician.
The Oncocerida comprise a diverse group of generally small nautiloid cephalopods known from the Middle Ordovician to the Mississippian, in which the connecting rings are thin and siphuncle segments are variably expanded. At present the order consists of some 16 families, a few of which, such as the Oncoceratidae, Brevicoceratidae, and Acleistoceratidae contain a fair number of genera each while others like the Trimeroceratidae and Archiacoceratidae are represented by only two or three.
The Tarphycerida were the first of the coiled cephalopods, found in marine sediments from the Lower Ordovician to the Middle Devonian. Some, such as Aphetoceras and Estonioceras, are loosely coiled and gyroconic; others, such as Campbelloceras, Tarphyceras, and Trocholites, are tightly coiled, but evolute with all whorls showing. The body chamber of tarphycerids is typically long and tubular, as much as half the length of the containing whorl in most, greater than in the Silurian Ophidioceratidae. The Tarphycerida evolved from the elongated, compressed, exogastric Bassleroceratidae, probably Bassleroceras, around the end of the Gasconadian through forms like Aphetoceras. Close coiling developed rather quickly, and both gyroconic and evolute forms are found in the early middle Canadian.
The Acleistoceratidae is a family of oncocerids that contains genera characterized by depressed exogastric brevicones and cyrtocones that range from the Middle Silurian to the Middle Devonian. The siphuncle is broadly expanded, and in some actinosiphonate.
The Brevicoceratidae is a family of oncocerids that contains genera characterized by exogastric gyrocones, brevicones, and torticones. that tend to develop vestigial actinosiphonate deposits and subtriangular transverse sections. The Brevicoceratidae are derived from Oonoceras (Oncoceratidae) and range from the mid-Silurian to the Upper Devonian.
Uranoceras is a barrandeocerid genus from the Middle Silurian belonging to the family Uranoceratidae, characterized by its loosely coiled, gyroconic shell of 1.5 to 2 subquadrate whorls.
Strophiceras is an extinct genus of cephalopods from the Order Nautilida, which includes, in a separate family, Nautilus and Allonautilus.
Triboloceras is the name given to an extinct nautiloid genus from the Lower Carboniferous (Mississippian), included in the nautilid family Trigonoceratidae characterized by an evolute shell bearing longitudinal ribs, with whorls in contact except in the early and very latest growth stages. Chambers are short, sutures tend for form ventral and in some cases dorsal and lateral lobes. The siphuncle is small, tubular, and subcentral.
Baltoceratidae is an extinct family of orthoconic cephalopods belonging to the subclass Nautiloidea endemic to what would be Asia, Australia, Europe, North America, and South America during the Ordovician living from about 480–460 mya, existing for approximately 20 million years .
Acleistoceras is a genus of the oncocerid, nautiloid family Acleistoceratidae that lived in the shallow seas that covered much of North America during the Devonian; living from 409—383.7 mya, existing for approximately 25.3 million years .
Orthoceratoidea is a subclass, formerly considered an infraclass or a superorder, that comprises Cephalopoda orders that have orthoconic to slightly cyrtoconic shells and central to subcentral siphuncles in which there may be internal deposits. Currently, Orthoceratoidea comprises the orders Dissidocerida, Ascocerida, Pseudorthocerida, Lituitida and Orthocerida.
The Graciloceratidae is a family of nautiloid cephalopods from the Middle and Upper Ordovician belonging to the Oncocerida, characterized by exogastric cyrtocones that expand slightly or moderately and have thin walled, orthochoanitic marginal or subventral, tubular siphuncles.
Oncoceratidae is a family of nauatiloid cephalopods in the order Oncocerida established by Hyatt, 1884, that range from the Middle Ordovician to the Upper Silurian.
The Bassleroceratidae is a family of gradually expanding, smooth ellesmerocerids with a slight to moderate exogastric curvature, subcircular to strongly compressed cross section, and ventral orthochaonitc siphuncle. The ventral side is typically more sharply rounded than the dorsal side and septa are close spaced. Connecting rings are thick and slightly expanded into the siphuncle, making the segments slightly concave; characteristic of the Ellesmerocerida.
Jolietoceras is a compressed, annulate, lituiconic nautiloid included in the derived Tarphycerid family, Uranoceratidae. The shell is gyroconic in the early stage, becoming straight and more rapidly expanded in the later. sutures are straight and transverse. Surface annuli slope strongly to the rear, dorso-ventrally, in the early gyroconic stage but a lacking in the later straight segment.
Cummingsoceras is a genus of barrandeoceroids within the Tarphycerida, included in the family Uranoceratidae. Its shell is a rapidly expanding gyrocone of about 1.5 narrowly separated whorls.
Cliftonoceras is a genus of barrandeoceroid type tarphycerids from the Uranoceratidae characterized by a smooth gyroconic shell with a rounded dorsum and flattened venter, and by a subvental siphuncle composed of thin connecting rings and necks that are straight ventrally, recumbent dorsally.
The Barrandeocerina comprise a suborder of Early Paleozoic nautiloid cephalopods, primitively coiled but later forms may be cyroconic, gyroconic, torticonic, and even breviconic, all having empty siphuncles with thin connecting rings. The Barrandeocerina were originally defined as a separate order by Rousseau Flower, but since then have been united within the Tarphycerida as a suborder. Derivation is from the Tarphyceratidae.
The Nephriticeratidae is a family of early Paleozoic nautilod cephalopods included in the Barrandeocerina, distinguished by mostly cyrtoconic as well as gyroconic, sepenticontic, and sinstrally torticonic shells with large, typically straight necked (orthchoanitic) siphuncles. As for the suborder, connecting rings are thin.
