Leangella (Leangella) cf. scissa ( Davidson, 1871 )

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 : 404

Leangella (Leangella) cf. scissa ( Davidson, 1871)

Fig. 8A .

Material.— Two specimens. Porkuni Regional Stage , Kuldiga Formation , Hirnantian (Upper Ordovician); western Latvia. Drill core and depth (in meters) of brachiopod samples: collection GIT 542 : Riekstini-15, 859.3, 861.8–861.85 .

Remarks.—Small, strongly concavo-convex shells, sub-triangular in outline with 5 primary ribs, similar to L. (L.) cf. scissa from the Dalmanitina Beds in Sweden ( Bergström 1968) and also to L. (L.) scissa from the lowermost Silurian in the East Baltic ( Rubel 2011). The larger of two specimens is 6.4 mm wide, 5.8 mm long and 2.9 mm deep, the smaller is only 1.5 mm wide. Cardinal angles rounded; anterior commissure slightly sulcate. Ventral interarea almost orthocline, slightly concave at the apex, 0.6 mm high. Delthyrium with small deltidial plates in apical part. Dorsal interarea flat, hypercline, 0.4 mm high. Notothyrium filled with trilobate cardinal process. Radial ornament of five primary and 4 additional ribs on ventral valve with very fine intercalated costellae. The Swedish species apparently differs from the Baltic material in lacking fine costellae between the primary costae; the Silurian L. (L.) scissa has a wider shell and more convex ventral valve.

Although rare in the Hirnantia brachiopod fauna, Leangella is common in the Boda Limestone ( Sheehan 1979; assigned to Diambonia, Jaanusson 1982 ). The species L. (L.) longae Cocks, 2005 from the lowermost Boda flank facies at Osmundsberget differs from the Hirnantian specimens in having more numerous (up to 14) primary costae.

The Hirnantian material of Leangella from the central Oslo Region in Norway, identified as L. aff. cylindrica ( Reed, 1917) by Cocks (1982), is insufficiently known for adequate comparison.

Figures

Fig. 8. Plectambonitoid brachiopods from the Kuldiga Formation of the Porkuni Regional Stage, Hirnantian (Upper Ordovician), East Baltic, western Latvia. A. Leangella sp., shell, GIT 542-222, Riekstini-15, depth 859.3 m, ventral (A1), dorsal (A2), and lateral (A3) views. B. Eoplectodonta sp., incomplete ventral valve, GIT 542-21, Stirnas-18, 911.9 m, ventral view.