Leangella (Leangella) Öpik, 1933

Musteikis, Petras & Cocks, L. Robin M., 2004, Strophomenide and orthotetide Silurian brachiopods from the Baltic region, with particular reference to Lithuanian boreholes, Acta Palaeontologica Polonica 49 (3), pp. 455-482 : 468-469

Leangella (Leangella) Öpik, 1933

Remarks.—The species recorded from the Silurian of Baltica are Leangella scissa ( Davidson, 1871) , Leangella triangularis ( Holtedahl, 1916) , and Leangella segmentum ( Lindström, 1861) . Leangella was erected by Öpik (1933: 42), with Plectambonites scissa var. triangularis Holtedahl, 1916 , from the Lower Llandovery of the Oslo region as its type. However, Cocks (1970) and Cocks and Rong (1989) did not recognize L. triangularis as a separate taxon, putting it within the synonymy of Leangella scissa . Later Baarli (1995: 24) distinguished L. triangularis as a valid and separate subspecies of L. scissa and the only Leangella in the Solvik Formation of the Oslo area; however, we do not follow Baarli’s differentiation and identify of all Baltic early Llandovery specimens, including those from the Lithuanian boreholes, as L. scissa . It occurs in the Dobelė Formation (Aeronian) in west Lithuania ( Figs. 2 , 3 ) in the Kurtuvėnai−161 (1478.9 m) and Šešuvis−11 (1620.1 m) boreholes. Rybnikova (1967: 186) recorded and illustrated L. scissa from the Lower and Middle Llandovery of Latvia.

Leangella segmentum is the only known species of the genus from the Wenlock or later rocks of Baltica, its type locality of Djupvik is within the Upper Wenlock Mulde Marl of Gotland, and the lectotype was selected by Cocks (1970:

MUSTEIKIS AND COCKS—SILURIAN BRACHIOPODS FROM THE BALTIC REGION 469

163) and the species further revised by Bassett and Cocks (1974: 13).We illustrate here ( Figs. 4A–D, 8R–T) specimens which were identified as L. segmentum from the Wenlock and Lower Ludlow of the Lithuanian boreholes. The species occurs in the Švenčionys (Telychian), Paprieniai, and Jonava Beds of the Birštonas formations (Sheinwoodian) in east Lithuania; in the Jūrmala (Telychian), Riga and Gėluva formations (Sheinwoodian and Homerian), Šešupė Beds of Dubysa Formation (Gorstian) in central Lithuania; the upper part of the Ragainė, the Siesartis (Homerian), and the lower part of Dubysa and the Rusnė formations (Gorstian) in west Lithuania. For localities see Appendix.

Figures

Fig. 2. Correlation of the Silurian of west, central and east Lithuania with the international Silurian stages, the East Baltic regional stages and the graptolite and conodont zones.

Fig. 3. Ranges of Silurian plectambonitoidean, strophomenoidean, and orthotetoidean brachiopods within the Lithuanian boreholes (see Appendix, Table 1 for details).