Cameroceras regulus ( Eichwald, 1860 )

Kröger, Björn, 2013, The cephalopods of the Boda Limestone, Late Ordovician, of Dalarna, Sweden, European Journal of Taxonomy 41, pp. 1-110 : 7-8

Cameroceras regulus ( Eichwald, 1860)

Endoceras regulus Eichwald, 1857: 177 .

Orthoceras turris Angelin in Angelin & Lindström, 1880: 6 , pl. 6, figs 14, 15.

Endoceras iucundum Stumbur, 1956: 182 , pl. 25, text-fig. 3, pl. 1, figs 4, 7, 8, pl. 2, figs 1, 3. Endoceras regulus – Eichwald 1860:1248, pl. 46, fig. 8.

Cameroceras regulus – Balashov 1968: 70, 101, pl. 5, fig. 3.

Diagnosis

Orthocones with a slightly depressed conch cross section; angle of expansion less than 5°; ornamented with fine transverse striae; sutures directly transverse, ca. seven chambers occur on a distance similar to the conch cross section; siphuncular diameter up to 0.5 of corresponding conch cross section; siphuncle marginal, in contact with shell wall; siphuncular segments slightly concave in longitudinal view; septal necks holochoanitic. (Adopted from Balashov 1968.)

Type locality and horizon

Kõrgesaare, Hiiumaa Island, Estonia; Vormsi Regional Stage, late Katian, Ordovician.

Material examined

One specimen ( NRM Mo 152350) from Ostbjörka, Dalarna, Boda Limestone; late Katian, Late Ordovician.

Description

The specimen is a portion of a phragmocone with a diameter of 72 mm and marginally positioned siphuncle 31 mm in diameter (ca. 0.43 of the corresponding conch cross section). Directly transverse septa are 18 mm apart (0.25 of the conch cross section). The conch surface is ornamented with irregularly spaced, widely rounded striae, and in parts a faint, narrowly spaced shallow longitudinal striation is also visible.

Remarks

The specimen described herein was first described and figured as Orthoceras turris Angelin in Angelin & Lindström, 1880 ; it is the only known specimen of this species. The specimen agrees in general conch shape and in ornamentation with C. regulus . The species C. regulus is based on a type from the Vormsi Formation, in which the shell preservation is poor compared with that of the Boda Limestone and faint details of the ornamentation are not preserved. Therefore, the faint longitudinal striation found in the specimen from the Boda Limestone is regarded here as a character that does not justify the distinction of two species, and O. turris is interpreted as a junior synonym of C. regulus .

Comparison

Endoceras landerense Foerste, 1935 is comparable to Cameroceras regulus with respect to the angle of expansion, chamber height and position and relative diameter of the siphuncle, but the details of the ornamentation of this species are not known.

Stratigraphic and geographic range

Vormsi Regional Stage, Estonia ( Balashov 1968), late Katian; Boda Limestone, late Katian, Siljan District, Sweden.