Jonesea Cocks and Rong, 1989

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 : 469-470

Genera Jonesea Cocks and Rong, 1989 and Aegiria Öpik, 1933

Remarks.—The species recorded from the Silurian of Baltica are Jonesea grayi ( Davidson, 1849) from the Lower Ludlow of Gotland ( Bassett and Cocks 1974: 13), Jonesea aknistensis ( Rybnikova, 1967) , and Aegiria norvegica Öpik, 1933 .

These small plectambonitoids, which can be very abundant at certain horizons from the Late Ordovician to the Ludlow, have often been assigned to Chonetoidea , but that genus is now known to be restricted to the Ordovician ( Cocks and Rong 2000).

Öpik (1933) erected the genus Aegiria , with the type species A. norvegica from the Lower Llandovery Solvik Formation of Leangen, Oslo, and which was revised by Baarli (1995: 26). However, Aegiria is not known from beds younger than the Lower Llandovery, and is not yet recorded from the East Baltic. Rybnikova (1967: 188) erected the new species Plectodonta aknistensis , with the holotype from the Upper Wenlock of the Akniste borehole in Latvia. Unfortunately only exteriors were figured by Rybnikova (1967), and we reillustrate her type specimen here ( Fig. 4E), but nevertheless the distinctive outline, profile and angular ribbing of this small species places it without doubt within the genus Jonesea . Plectodonta itself is known only from the Lower Devonian of Podolia, Ukraine, and its type species was also reillustrated by Cocks and Rong (1989). Although Cocks and Rong (1989: 127) doubtfully referred Plectambonites aequalis Teichert (1928) , from the Lower Llandovery Tamsalu Formation of Estonia, to Jonesea , we now think that that species is more likely to belong to the strophomenoid Eopholidostrophia (see above). Thus the only recorded species of Jonesea from Baltica, apart from J. aknistensis , is the type species, J. grayi ( Davidson, 1849) , whose type locality is in the Wenlock of England. Baltic J. grayi has not previously been illustrated, merely listed (e.g., by Modzalevskaya and Pushkin 1989: 96, from the Ludlow of Belarus, and Rubel et al., 1984: 12) from the East Baltic. Jonesea occurs in the Lithuanian boreholes sporadically in the Upper Llandovery, Wenlock and Ludlow: a few specimens are also recorded from the Lower Pridoli (Minija Formation in the Bebirva−110 borehole): we identify it as J. grayi by comparison with English material. More revision of the East Baltic material is necessary, but there are few interiors recorded from the East Baltic, and we can only illustrate an exterior here ( Fig. 4F). Since the interiors of J. aknistensis are not known, we provisionally place the species within the synonymy of the very variable J. grayi until more data and specimens become available.

Lithuanian distribution of Jonesea grayi is in the Šenčionys (Telychian), Paprieniai (Sheinwoodian) and Jonava Beds of Birštonas formations (Sheinwoodian) in east Lithuania; the Jūrmala (Telychian), Riga and Gėluva (Sheinwoodian and Homerian) formations in central Lithuania; the Dobelė (Aeronian), Jūrmala (Telychian), Riga, Ragainė and Siesartis (Sheinwoodian and Homerian), Rusnė, Dubysa, Mituva and Pagėgiai (Gorstian and Ludfordian) and Minija (Lower Pridoli) formations in west Lithuania (Appendix)