Liroceras Teichert, 1940

Korn, Dieter & Klug, Christian, 2023, Early Carboniferous coiled nautiloids from the Anti-Atlas (Morocco), European Journal of Taxonomy 885, pp. 156-194 : 177-178

Genus Liroceras Teichert, 1940

Type species

Coloceras liratum Girty, 1911 ; original designation.

Diagnosis

Genus of the family Liroceratidae with pachyconic to globular, involute or subinvolute conch; umbilicus closed by a plug in some species. The first whorl is 10–20 mm in diameter with a very small umbilical foramen; the conch is rapidly increasing in height with a high coiling rate (WER usually higher than 2.50). Whorls weakly embracing, their profile ranges from reniform to nearly circular. Juvenile conch with longitudinal ridges; adult ornament with growth lines with a fairly deep ventral sinus and spiral lines around the umbilicus in some species. Septa without inflexions, slightly concave. Suture line simple, nearly straight to straight with a shallow, broadly rounded internal lobe. The siphuncle has a position between the centre of the aperture and the venter (after Gordon 1965; Shimansky 1967).

Included Early Carboniferous species

Species of Liroceras are known from the Early Carboniferous to the Late Permian. Shimansky (1967: 194) and Gordon (1965: 156) provided species lists of the genus, several of which are also known from the Early Carboniferous:

Northern and Central Europe ( Trenkner 1868; Miller et al. 1933; Schmidt 1951; Turner 1954; Ramsbottom & Moore 1961): Nautilus Grundensis Trenkner, 1868 , Harz Mountains; Coloceras hyatti Miller, Dunbar & Condra, 1933 , Belgium; Liroceras occlusor Schmidt, 1951 , Harz Mountains; Liroceras schaelkense Schmidt, 1951 , Rhenish Mountains; Liroceras lunense Turner, 1954 , Yorkshire; Liroceras leitrimense Ramsbottom & Moore, 1961 , Ireland.

North Africa (this paper): Liroceras vermis sp. nov.; Anti-Atlas; Liroceras karaouii sp. nov., Anti-Atlas.

Western Russia and Urals ( Eichwald 1857; Shimansky 1967): Nautilus excentricus von Eichwald, 1857 , western Russia; Liroceras fornicatum Shimansky, 1967 , western Russia; Liroceras praelunense Shimansky, 1967 , North Urals; Liroceras ruzhencevi Shimansky, 1967 , South Urals.

North China ( Ruan & Zhou 1987): Liroceras reniforme Ruan & Zhou, 1987 , Ningxia.

Remarks

Liroceras is a genus with a wide stratigraphic range, extending from the Viséan to the latest Permian. Gordon (1965) and Shimansky (1967) compiled species lists; these demonstrate the wide stratigraphic and geographic distribution. In contrast, the morphological range within the genus is small; the conchs of all species are very similar and differ mainly in the width of the umbilicus and in the formation of spiral lines. The most similar genus is Bistrialites Turner, 1954 , but in this genus the umbilical margin is more angular, in contrast to Liroceras with a rounded or subangular umbilical margin.