Dubaria tenera Nikiforova & T. Modzalevskaya, 1968

Modzalevskaya, Tatiana L., 2003, Silurian and Devonian brachiopods from Severnaya Zemlya (Russian Arctic), Geodiversitas 25 (1), pp. 73-107 : 93-94

Dubaria tenera Nikiforova & T. Modzalevskaya, 1968 ( Figs 22 J-M; 23)

Dubaria tenera Nikiforova & T. Modzalevskaya, 1968: 68 , pl. III, figs 8-10.

MATERIAL EXAMINED. — Three specimens from loc. 13, beds 64, 89, Matusevich River, October Revolution Island ( Männik et al. 2002: figs 2, 5); Vodopad and Golomyannyj formations.

REMARKS

The specimens assigned to this species show some characteristics of external and internal structures identical to those of Dubaria tenera , illustrated by Nikiforova & Modzalevskaya from the Talikit Formation of East Siberia ( Fig. 23 ). Possibly, this species is a junior synonym of Atrypopsis varians Poulsen, 1943 described from the Offley Island Formation of Greenland ( Poulsen 1943: 44, pl. 5, figs 13-16). These two taxa are morphologically very similar. However, the identification of our specimens is quite problematic due to the lack of the dorsal myophragm on them. This structure is one of the main diagnostic features of Atrypopsis and Dubaria Boucot, Johnson & Staton, 1964 ( Rubel 1970) . P. Copper (1991: 37), restudying the atrypids, concluded that Atrypopsis , Dubaria , Rhynchatrypa Siehl, 1962 , and Barkolia Zhang, 1983 are junior synonyms of Septatrypa Kozlowski, 1929 . Hence, the occurrence of a short dorsal septum is an essential feature to identify Septatrypa ( Nikiforova et al. 1985: 44, pl. 11, fig. 9).

Order SPIRIFERIDA Waagen, 1883

Figures

FIG. 22. — A-D, Hyattidina remota n. sp.; A, ventral view; B, dorsal view; C, anterior view of a complete shell (holotype N 58/12991); D, lateral view of a complete shell (N 59/12991), loc. 13, bed 48, Golomyannyj Formation; E-H, Greenfieldia orbiculata n. sp.; E, ventral view; F, dorsal view; G, lateral view; H, anterior view of a complete shell (holotype N 62/12991), loc. 2, bed 66, Samojlovich Formation; I, Meristina? norilica (Nikiforova in Nikiforova & Andreeva, 1961), ventral view of a complete shell (N 61/12991), loc. 13, bed 27, Srednij Formation; J-M, Dubaria tenera Nikiforova & T. Modzalevskaya, 1968; J, ventral view; K, dorsal view; L, lateral view; M, anterior view of a complete shell (N 57/12991), loc. 13, bed 89, Vodopad Formation. Scale bars: A-C, E-H, 5 mm; D, J-M, 3 mm; I, 6 mm.

FIG. 23. — Selected transverse serial sections, illustrating the development of internal structures in Dubaria tenera Nikiforova & T. Modzalevskaya, 1968 (N 15/12991). Measurements: length 5.6 mm, width 8.0 mm, thickness 4.5 mm; loc. 13, bed 64, Golomyannyj Formation. Numerical designations are the same as on Fig. 11. Scale bar: 10 mm.