Orthoceras regulare Schlotheim, 1820

Kröger, Björn, 2004, Revision of Middle Ordovician orthoceratacean nautiloids from Baltoscandia, Acta Palaeontologica Polonica 49 (1), pp. 57-74 : 59-60

publication ID

https://doi.org/ 10.5281/zenodo.13272378

persistent identifier

https://treatment.plazi.org/id/03F28786-B171-FF93-FCAE-F9B16A42DFB0

treatment provided by

Felipe

scientific name

Orthoceras regulare Schlotheim, 1820
status

 

Orthoceras regulare Schlotheim, 1820 View in CoL

Fig. 2B View Fig .

Orthoceras regulare Schlotheim View in CoL ; Troedsson 1931: 13–16, 24–29 [cum syn.]

Material.— Forty specimens housed in the NRM, NMB, MMW, and GIH (in a large part the material of Troedsson 1931 a). Many of these specimens preserve the adult chambers of the phragmocone and the living chamber; sometimes the recrystallized shell is preserved.

Description.— Orthoceras regulare was described in great detail by Troedsson (1931). The current description is therefore mainly an abstract of Troedsson’s work supplemented by some new measurements and observations.

Conch form: The conch shows a circular cross section. With a maximum diameter: 40 mm, mean diameter of last chamber of the adult phragmocone: 25 mm (max: 29 mm, min: 19 mm) it is the largest Orthoceras . The conch shows an apical angle of 1.7–2.9° (mean e: 2.3°).

Ornamentation: The shell displays fine, narrowly spaced transverse striae; the elevated space between the striae appear imbricated and flat in nearly mature and mature specimens, and is sharp and acute in the juvenile parts of the shell. In addition to the transverse ornamentation, very minute longitudinal striae form a net−like ornamentation only detectable in well preserved specimens. The transverse banding forms an adapical lobe on the ventral side. The inner part of the shell is smooth, sometimes irregularly punctured. The cast shows a normal line at the ventral side of the phragmocone.

Phragmocone: Chambers 0.5 (mean) of the respective diameter in high. Sutures straight and septa concave. Cast of the mural areas displays fine longitudinal lines. Septal necks orthochoanitic. The central to subcentral tubular siphuncle shows a diameter of 0.15 (0.14–0.17) of the respective diameter of the conch. Endosiphuncular lining has been observed in the more apicad parts of the phragmocone (see Fig. 2B View Fig ). The deposits are more strongly developed in the ventral part of the shell.

Living chamber: The long adult living chamber is conical in shape. Three equiangularly arranged longitudinal impressions are found at about one third of the length of the adult living chamber. The impressions vary slightly in general shape but strongly in length (15–50 mm). They form 1–7 mm deep elongated notches in the shell. The conch at the position of the impressions is slightly constricted. The aperture widens rapidly orad of the constriction.

Distribution.— Orthoceras regulare occurs in the Seby and Folkeslunda Limestone (Lasnamägian) and in the Persnäs Limestone (Uhakuan) of Öland. It is also found in the Upper Grey Limestone (Lasnamägian) of the erratics of northern Germany and Poland.

NRM

Swedish Museum of Natural History - Zoological Collections

NMB

Naturhistorishes Museum

Kingdom

Animalia

Phylum

Mollusca

Class

Cephalopoda

Order

Orthocerida

Family

Orthoceratidae

Genus

Orthoceras

Loc

Orthoceras regulare Schlotheim, 1820

Kröger, Björn 2004
2004
Loc

Orthoceras regulare

Troedsson, G. T. 1931: 13
1931
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