Cameroceras hasta (Eichwald, 1857)

Figs 5A–B, 6

Endoceras hasta Eichwald, 1857: 194.

Endoceras magnum Stumbur, 1956: 182–183, pl. 3 figs 2–3, text-fig. 4.

Rossicoceras pirguense Balashov, 1968: 113, pl. 15 figs 3–4.

Endoceras novomagnum Greenfield, 2023: 1790.

Endoceras hasta – Eichwald 1860: 1247, pl. 46 fig. 7a–b.

Endoceras megastoma – Teichert 1930: 270, 273, pl. 5 fig. 1, text-fig. 2 (with synonymy).

Rossicoceras hasta – Balashov 1962a: pl. 4 fig. 4; 1968: 112, pl. 15 figs 1–2; 1974: 794, pl. 4 fig. 4. ― Saladzius 1966: 36, pl. 6 fig. 2. ― Dzik 1984: 35, text-fig. 7.32.

Endoceras magnum – Balashov 1968: 70.

Cameroceras hasta – Kröger 2013: 6–7, fig. 3.

Diagnosis

Smooth orthocones with a slightly depressed conch cross section; angle of expansion less than 5°; sutures directly transverse, seven or more chambers occur on a distance similar to the conch cross section; siphuncular diameter ca 0.5 of corresponding conch cross section; siphuncle slightly removed from conch wall; siphuncular segments slightly concave in lateral view; septal necks holochoanitic; endosiphocones form central spiculum. (Compiled from Balashov 1968.)

Material examined

ESTONIA • 2 specs; Hiiumaa Island, Kõrgessaare quarry; Vormsi Regional Stage; GIT 426-549, GIT 426-1111 • 4 specs; Paluküla quarry; Kõrgessaare Formation, Vormsi Regional Stage; GIT 426-575, GIT 426-1102, 426-1104, GIT 878-127 • 1 spec.; Vormsi Island, Saxby old quarry; Kõrgessaare Formation, Pirgu Regional Stage; TUG 1745-240 • 1 spec.; Saaremõisa (Lyckholm); Kõrgessaare Formation, Vormsi Regional Stage; TUG 42-373 • 1 spec.; Vormsi Island, Saxby shore, Kõrgessaare Formation, Vormsi Regional Stage; GIT 878-42 • 1 spec. from an unspecified locality at Vormsi Island, Kõrgessaare Formation, Vormsi Regional Stage; TUG 1650-1.

Type locality and horizon

Saaremõisa (Lyckholm), N of Haapsalu, western Estonia; Kõrgessaare Formation, Vormsi Regional Stage, late Katian, Ordovician.

Description

Two specimens are relatively long, and well-preserved fragments of the phragmocone:

Specimen TUG 1745-240 (Fig. 5B) is a fragment of a phragmocone, which is slightly deformed and in which the outer shell is not preserved. The conch cross section was apparently circular. The conch height is 43–62 mm at a length of 125 mm (angle of expansion 9°). The sutures are narrowly spaced (at conch height 48 mm with chamber length of 4 mm, at conch height 62 mm with chamber length 5.5 mm, RCL = 0.08–0.09) and are directly transverse. At a conch height of 62 mm, the siphuncle is 7 mm from the conch margin, and 28 mm high (RSP = 0.21, RSH = 0.45). Where visible, the septal necks are holochoanitic. At a conch height of 45 mm, a symmetric endosiphocone is preserved, which has its tip at ca mid-height of the siphuncle, and which is ca 35 mm long. A similar symmetrical endosiphocone is preserved in specimen GIT 426-574 where the conch height is ca 50 mm, the siphuncular diameter is 21 mm. There, the cone is ca 45 mm long.

Specimen TUG 42-373 (Fig. 5A) is a well-preserved part of a phragmocone with a circular conch cross section and with parts of the smooth outer shell preserved. The conch has a diameter of 60–78 mm over a length of 110 mm (angle of expansion = 9°). The sutures are straight and directly transverse; at a conch height of 67 mm they are 8 mm apart (RCL = 0.12). The siphuncle is 33 mm heigh, where the conch height is 78 mm and positioned ca 15 mm from the conch margin (RSP = 0.33).

A compilation of measurements of the relative chamber length (RCL) and the relative siphuncular position (RSP) of the Estonian material shows the variability of respective values, resulting in a mean RCL of 0.09 (n= 10), and mean RSP of 0.24 (n = 7), respectively (Fig. 6).

Remarks

The species diagnosis given in Kröger (2013) was based on Balashov’s (1968) description of the holotype, in which the latter states that in the holotype, seven chambers occur per distance similar to the conch cross section (RCL ca 0.14). This is in contradiction to the figured holotype (Balashov 1968: pl. 15, fig. 1), where the RCL can be measured as ca 0.11. The RCL of the measured holotype is larger than the mean of the RCL’s from the material examined herein (RCL = 0.09) but still well within its variability (0.06–0.12). This applies also for the specimens assigned to C. hasta from the Boda Limestone, Sweden (Kröger 2013: 7). Accounting for this variability, the diagnosis given in Kröger (2013) is herein slightly emended with respect the relative chamber length.