The Lamellorthoceratidae is a family of fossil nautiloid

Nautiloid

Nautiloids are a large and diverse group of marine cephalopods belonging to the subclass Nautiloidea that began in the Late Cambrian and are represented today by the living Nautilus. Nautiloids flourished during the early Paleozoic era, where they constituted the main predatory animals, and...

s in the Orthocerida

Orthocerida

Orthocerida is an order of extinct nautiloid cephalopods also known as the Michelinocerda that lived from the Early Ordovician possibly to the Late Triassic . A fossil found in the Caucasus suggests they may even have survived until the Early Cretaceous...

, defined by Curt Teichert in 1961. The lamellorthoceratids are placed in the superfamily Orthocerataceae

Orthocerataceae

The Orthocerataceae is a superfamily of orthocerid cephalopods that lived from the late Early Ordovician to the Early Cretaceous., but is no longer in general use....

 in the Treatise on Invertebrate Paleontology

Treatise on Invertebrate Paleontology

The Treatise on Invertebrate Paleontology published by the Geological Society of America and the University of Kansas Press, is a definitive multi-authored work of some 50 volumes, written by more than 300 paleontologists, and covering every phylum, class, order, family, and genus of fossil and...

 (Walter Sweet,1964).

The Lamellorthoceratidae are distinguished by cameral deposits consisting of simple or bifurcating epispetal, or rarely hyposeptal lamellae, set radially with respect to the siphuncle

Siphuncle

The siphuncle is a strand of tissue passing longitudinally through the shell of a cephalopod mollusk. Only cephalopods with chambered shells have siphuncles, such as the extinct ammonites and belemnites, and the living nautiluses, cuttlefish, and Spirula...

; often filling the entire posterior part of the shell. Lamellorthoceratid shells are straight or slightly endogastric with a slender, cylindrical subcentral orthochoanitic siphuncle, free or organic deposits.

The Lamellorthoceratidae are known from the Lower and Middle Devonian

Devonian

The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...

 and possibly from the Lower Carboniferous

Carboniferous

The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...

, and is represented by three genera.

Genera of the Lamellorthoceratidae

Lamellorthoceras, a lamellorthoceriatic from the lower and middle Devonian of North Africa (Algeria, Morocco) characterized by radial lamellae that tend to be wavy, twisted, or to have bifurcating inner edges. All chambes may be filled. Otherwise the genus is similar to Arthrophyllum (below). Lamellorthoceras was named and described by Termier & Termier in 1950.

Arthrophyllum (not the plant) . Slender, gradually expanding orthocones or faintly endogastic longicones, the surfaces of which are covered with close spaced sinuous transverse crenulations that form broad dorsal and vental salients and lateral sinuses. Septa are shallow, sutures straight and transverse. Camerae contain episeptal deposits formed by longitudinal lamellae that radiate inwardly from the chamber walls and increase in bulk adapically so as to completely fill the entire apical chambers.
Arthrophyllum was named and described by Beyrich in 1850 and is known from the Lower Devonian of Europe (France, Germany, Turkey). Tentative specimens are known from the Lower Carboniferous.

Gorgonoceras. Similar to Arthrophyllum except that the surface has faint longitudinal ribs, the eccentric siphuncle has a continuous endsiphuncular lining on the ventral side, and there is a ventral lamella that is much thicker than the other. Gorgonoceras is known from the Middle Devonian of the Sverlovsk district in Russia and was named and described by Zhuravleva in 1961.