Stegerhynchus, Foerste, 1909

Modzalevskaya, Tatiana L., 2003, Silurian and Devonian brachiopods from Severnaya Zemlya (Russian Arctic), Geodiversitas 25 (1), pp. 73-107 : 85-87

Stegerhynchus ? decemplicatus duplex Nikiforova & T. Modzalevskaya, 1968 ( Figs 14 A-E; 15)

Stegerhynchus decemplicatus duplex Nikiforova & T. Modzalevskaya, 1968: 54 , pl. I, figs 4-7.

Stegerhynchus (Stegerhynchus) decemplicatus duplex – Lopushinskaya & Yadrenkina 1987: 119, pl. 25, fig. 6. MATERIAL EXAMINED. — 16 specimens and fragments from loc. 13, bed 89, Matusevich River, October Revolution Island ( Männik et al. 2002: figs 2, 5); Vodopad Formation.

REMARKS

The discrete cardinal plate supported by a massive dorsal platform, median elevation strengthened by shell thickening and merging with a low broad septum or myophragm are the characteristic features of Stegerhynchus ( Fig. 15 ). The linear cardinal process is absent, probably due to the poor preservation. The outline, size, two ribs in the ventral sinus, three ribs on the dorsal fold, and well preserved concentric ornament of the specimens suggest that these specimens can be refered to S.? decemplicatus duplex Nikiforova & T. Modzalevskaya, 1968 described from the Talikit, Omnutakh, and Meik formations of East Siberia. Small size, and weakly developed sinus and fold distinguish a somewhat similar genus Nikolaevirhynchus Baranov, 1988 identified from Ryabininskaya Formation (Wenlock) on North East Russia. Moreover, the representatives of genus Nikolaevirhynchus are characterized by an absence of the median longitudinal elevation, which is broadened posteriorly and strengthened by shell thickening.

Family TRIGONIRHYCHIIDAE McLaren, 1965

Figures

FIG. 14. — A-E, Stegerhynchus? decemplicatus duplex Nikiforova & T. Modzalevskaya, 1968; A, ventral view; B, dorsal view; C, lateral view; D, anterior view; E, enlarged external surface of a complete shell (N 38/12991), loc. 13, bed 89, Vodopad Formation; F-I, V, Anabaria? latens n. sp.; F, dorsal view; G, ventral view; H, lateral view; I, anterior view of a complete shell (holotype N 50/12991), loc. 11, bed 6B, Samojlovich Formation; V, enlarged external surface of a poorly silicified shell (N 51/12991), loc. 29a,?Vodopad Formation; J-P, R, S, Lenatoechia octjabrensis n. sp.; J, ventral view; K, dorsal view; L, lateral view; M, anterior views of a complete shell (N 41/12991), loc. 11, bed 6B, Samojlovich Formation; N, ventral view; O, dorsal view; P, lateral view of a complete shell (holotype N 40/12991), loc. 2, bed 66, Samojlovich Formation; R, ventral view; S, dorsal view of complete shell (N 42/12991), loc. 117v,?Samojlovich Formation; Q, T, U, Anabaria? latens n. sp.; Q, pedicle valve of a complete shell (N 52/12991), loc. 13, bed 27, Srednij Formation; T, ventral view; U, dorsal view of a complete shell (N 53/12991), loc. 13, bed 64, Golomyannyj Formation. Scale bars: A-D, F-M, 5 mm; E, V, 2 mm; N-U, 3 mm.

FIG. 15. — Selected transverse serial sections, illustrating the development of internal structures in Lenatoechia octjabrensis n. sp. (N 43/12991). Measurements: length 8.1 mm, width 8.2 mm, thickness 5.9 mm; loc. 2, bed 66, Samojlovich Formation. Numerical designations are the same as on Fig. 11. Scale bar: 3 mm.