Fig. 3
Endoceras hasta Eichwald, 1857: 194.
Rossicoceras pirguense Balashov, 1968: 113, pl. 15, figs 3, 4.
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 1962: 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.
Smooth orthocones with a slightly depressed conch cross section; angle of expansion less than 5°; sutures directly transverse, ca. seven 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 with SPR of 0.1; siphuncular segments slightly concave in longitudinal view; septal necks holochoanitic; endosiphocones form central spiculum (compiled from Balashov 1968).
Saaremõisa, western Estonia, Vormsi Regional Stage, late Katian Ordovician.
Four specimens ( PMU 26609 –26612) from Kallholn, Dalarna, Boda Limestone; late Katian, Late Ordovician.
This species was described in detail by Teichert (1930) and Balashov (1968). The specimen from the Boda Limestone adds some detail with regard to the variability of some characters. The chamber height in the four measured specimens varies from ca. 0.1 to 0.2 of the corresponding conch cross section, the siphuncular diameter varies from 0.42 to 0.5, and the distance of the siphuncle from the conch margin is 0.09–0.11 of the corresponding conch cross section ( Fig. 3). In specimen PMU 26611, parts of the external shell are preserved, but the preservation is relatively poor and no ornamentation is visible on the surface.
Balashov (1968) distinguished R. pirguense from R. hasta mainly on the position of the siphuncle, which should be closer to the conch margin in R. pirguense. However, the information given in the original species description is ambiguous. The measurements provided in the text ( Balashov 1968: 113) reveal a relative distance which is nearly identical to that of R. hasta. Based on these measurements and the original figures, R. hasta and R. pirguense are indistinguishable and R. pirguense must be regarded as a junior synonym of R. hasta.
Cameroceras turrisoides sp. nov. differs from this species in having a narrower siphuncle (ca. 0.3–0.4 of the corresponding conch cross section) and a siphuncle which is closer to the conch center (SPR ca. 0.2; Fig. 3).
Cameroceras regulus ( Eichwald, 1860) from the Vormsi Regional stage of Estonia differs in having a slightly larger siphuncle (0.5 of conch cross section) in contact with the conch margin. Endoceras coxi Foerste & Cox, 1936, from the latest Katian of Akpatok Island of the Canadian Arctic, is similar to C. hasta with respect to the relative diameter of the siphuncle and the relative distance of the siphuncle from the conch margin. Consequently, this species must be assigned within Cameroceras. The chamber spacing of Cameroceras coxi (Foerste & Cox, 1936) comb. nov. (ca. 3.6 chambers in a distance corresponding to the conch diameter) is not within the range of variance of C. hasta.
Vormsi and Pirgu Regional Stage, Estonia, Lithuania ( Saladzius 1966; Balashov 1968), late Katian, Taymyr, Russia ( Balashov 1968); Boda Limestone, late Katian, Siljan District, Sweden.