Strandoceras sphinx ( Schmidt, 1858 )

Kröger, Björn, 2013, The cephalopods of the Boda Limestone, Late Ordovician, of Dalarna, Sweden, European Journal of Taxonomy 41, pp. 1-110 : 16-17

Strandoceras sphinx ( Schmidt, 1858)

Fig. 7E

Phragmoceras sphynx Schmidt, 1858: 200 .

Protophragmoceras sphinx – Teichert 1930: 270, 299-301, pl. 7, fig. 20, pl. 8, fig. 24, text-figs 3, 4. ― Dzik 1984: 48, 52, 65, text-fig.14.5, pl. 7, fig. 7.

Protophragmoceras sphynx – Strand 1934: 93.

Strandoceras sphynx – Flower in Flower & Teichert 1957: 57, 114, text-figs 15e, g-h.

Strandoceras sphinx – Balashov 1975: 69, pl. 2, fig. 1.

Diagnosis

Strandoceras with moderate curvature, angle of expansion 16–19°; compressed conch cross section with width/height ratio of 0.8–0.9; body chamber long, reaching 0.4 of total conch length; ornamented with distinctive transverse rounded striae, which form shallow sinuses on the anti- and prosiphuncular side of the conch. (Adopted from Strand 1934 and Dzik 1984.)

Type locality and horizon

“Setlep”, Island Vormsi, Estonia, Vormsi/Pirgu Regional Stage (“Lyckholm stage”, Teichert 1930), late Katian, Ordovician.

Material examined

Three specimens ( PMU 26629–26631) from Kallholn, Dalarna, Boda Limestone; one specimen ( PMU 26632) from Amtjärn, Dalarna, Johnstorp Formation. All late Katian, Late Ordovician.

Description

The largest specimen, PMU 26629, is a piece of phragmocone, measuring 74– 48 mm in height, and with a maximum width of 63 mm (width/height ratio 0.85) and expanding at an angle of 19° ( Fig. 7E ). The conch cross section is broadly rounded on the antisiphuncular side and forms a characteristic narrow subangular margin on the prosiphuncular side. Adorally the siphuncle measures ca. 6 mm in diameter (0.08 of conch height) and is almost marginal in position on the concave side of the conch. The septa are narrowly spaced at a distance of ca. 8 mm (ca. 0.11 of corresponding conch height) in the adoral part of the fragment. The sutures are directly transverse. The conch surface is ornamented with fine, relatively widely spaced rounded transverse striae, distance between striae is ca. 3 mm at the adoral part of the fragment. The striae form a broadly curved lateral salient and shallow sinuses on the pro-, and antisiphuncular sides.

A second specimen, PMU 26631, consists of a portion of phragmocone with a conch height of 16 mm apically. Shallow rounded striae ca. 0.7 mm in width are displayed on the apical part of the phragmocone. These are almost directly transverse, but form shallow sinuses on the the pro-, and antisiphuncular sides of the conch.

Remarks

The specimens from the Boda Limestone are very similar to the specimen described and figured from the Vormsi/Pirgu Regional Stage of Estonia (“Lyckholm stage” of Teichert 1930: pl. 8, fig. 24) which has a width/height ratio of the conch of 0.76, an apical angle of ca. 16° and a similar ornamentation and curvature.

Comparison

S. strandi Sweet, 1958 differs from S. sphinx in its more compressed conch cross section (width/height = 0.68). S. tyriense differs from S. sphinx in its smaller adult size (ca. 60 mm conch height) and stronger curvature of the conch.

Stratigraphic and geographic range

Upper Herøya Formation (“Gastropod Limestone”), Skien-Langesund district, Norway ( Strand 1934); erratic limestone boulders from Vormsi/Pirgu Regional Stage, Zgierz, Poland ( Dzik 1984); Vormsi/Pirgu Regional Stage (“Lyckholm stage”), Estonia ( Teichert 1930); Molodov Horizon, Podolia ( Balashov 1975); Johnstorp Formation (“Grey Tretaspis Shale”), Boda Limestone, Dalarna, Sweden; all late Katian.

Figures

Fig. 7. Breviconic cephalopods of the Boda Limestone and details of an endocerid. A. Dalecarlioceras constrictum Frye, 1987, PMU 24777, holotype, Kallholn. B. Dalecarlioceras dalecarlicum (Frye, 1987) comb. nov., PMU 24774, holotype, Kallholn. C. Cyrtorizoceras thorslundi sp. nov., PMU 26658, Kallholn; note the morphological transition between D. constrictum and C. thorslundi sp. nov.; the adult size increases in Dalecarlioceras and the mature body chamber is gibbous. D. Cameroceras turrisoides sp. nov., PMU 26623, Osmundberget, lateral view of apical fragment with abrupt transition between embryonic and juvenile conch. E. Strandoceras sphinx (Schmidt, 1858), PMU 26629, Kallholn. Scale bars: A-C, E = 10 mm; D = 10 mm.