Eostropheodonta cf. parvicostellata Rong, 1984

Hints, Linda & Harper, David A. T., 2015, The Hirnantian (Late Ordovician) brachiopod fauna of the East Baltic: Taxonomy of the key species, Acta Palaeontologica Polonica 60 (2), pp. 395-420 : 402-403

Eostropheodonta cf. parvicostellata Rong, 1984

Figs. 6B, E .

Material.— Six specimens embedded in rock. Porkuni Regional Stage , Kuldiga Formation , Hirnantian ( Upper Ordovician ); western Latvia. Drill core and depth (in meters) or sample intervals with brachiopods. Collection GIT 542 : Adze, 844.2; Aispute-41, 995.9; Riekstini-15, 850.0; Vilcini-19, 894.7–906.4; collection LDM G: Priekule-23, 1395.6 .

Remarks.—Some specimens, amongst those assigned to the genus Eostropheodonta , are particularly distinctive, having a parvicostellate ornament of fine costae and costellae of nearly equal strengths, 9–11 costellae per 2 mm at 5 mm from umbo. The shells are small up to 13 mm wide at the hinge line and about 9 mm long. Cardinal extremities are acute. Ventral interarea is 0.3 mm high, delthyrium is open ( Fig. 6B 1). Dorsal valve is flat, interarea low, notothyrium covered by small, convex chilidium. The radial ornament of these Baltic specimens is most similar to E. parvicostellata from the Hirnantian of China ( Rong 1984). However, our specimens are relatively small. The lack of interiors negates precise species level identification. E. parvicostellata differs

HINTS AND HARPER— HIRNANTIAN BRACHIOPODS FROM EAST BALTIC 403

B1 2 mm 5 mm A 1 A 2 C 1 1 mm A 3 1 mm 2 mm B2 5 mm C 2 2 mm D 5 mm

from E. h. hirnantensis in having a median process between the cardinal process lobes ( Rong 1984: fig. 15). However, the very high variability of radial ornament of the latter species ( Rong and Cocks 1994) does not exclude possible assignment to E. h. hirnantensis .

Figures

Fig. 6. Leptostrophiid brachiopods from the Kuldiga Formation of the Porkuni Regional Stage, Hirnantian (Upper Ordovician), East Baltic, western Latvia A–E, G) and southwestern Estonia (F). A. Eostropheodonta hirnantensis (M`Coy, 1851), Taagepera, depth 413.9 m, moulds of ventral valves, GIT 542-337/1 A1) and GIT 542-337/2 (A2), exterior views. B, E. Eostropheodonta cf. parvicostellata Rong, 1984. B. Shell, GIT 542-381, Vilcini-19, 906.4 m, exterior view of dorsal valve (B1) and view on interarea (B2). E. Mould of dorsal valve, LDM G328-12, Priekule-33, 1395.6 m, exterior view. C, D, F, G. Coolinia sp. C. Mould of ventral valve, LDM G328-26, Dižrungi-17, 984.5 m, exterior view. D. Ventral valve, LDM G328-26, Dizrungi-17, 984.5 m, exterior view. F. Fragment of dorsal valve, GIT 542-364, Ruhnu-500, depth 612.9 m, view of cardinalia (F1) and exterior view (F2). G. Incomplete ventral valve, GIT 542 48-2, Stirnas-18, 899.0 m, interior view. Scale bars 2 mm.