Glyptohallicardia multicostata, Jagt-Yazykova & Krawczyński & Rakociński, 2006

Jagt-Yazykova, Elena, Krawczyński, Wojciech & Rakociński, Michał, 2006, Molluscs from the Early Frasnian Goniatite Level at Kostomłoty in the Holy Cross Mountains, Poland, Acta Palaeontologica Polonica 51 (4), pp. 707-718 : 716

Glyptohallicardia multicostata sp. nov.

Fig. 6A–F .

Holotype: GIUS 4−2290 Kos−20 ( Fig. 6A ).

Type horizon: Goniatite Level at the uppermost part of the Szydłówek Beds; Palmatolepis transitans conodont Zone, Early Frasnian.

Type locality: Active quarry Kostomłoty II (Małe Górki).

Derivation of the name: From Latin multus —numerous and costa —rib.

Diagnosis.— G. multicostata sp. nov. markedly differs from species with similar shell proportions, such as G. conversa , G. palmata , G. ruppachensis ( Beushausen, 1895) , G. eifeliensis ( Beushausen, 1895) , and G. aquarum ( Holzapfel, 1895) , as well as from other species of the genus Glyptohallicardia by a much larger number of radial ribs (24–29) on the shell surface.

Material.—Eighty well−preserved and almost 120 fragments of pyritised internal moulds and two internal moulds with preserved fragments of shells (GIUS 4−2290 Kos−20, 4−2291 Kos−21, 4−2292 Kos−22,4−2579 Kos−46/1–2,4−2847 Wz−41a/1).

Description.—Shell equivalve, inequilateral, moderately small (dimensions of holotype (mm): height = 2.5; length = 2.7; width/2 = 1.0), strongly inflated, ovate in outline and slightly elongated towards the postero−ventral margin. Prosogyrate umbilicus moderately large, slightly anterior in position. Hinge margin long, straight without visible hinge teeth. Ligament area narrow posteriorly and enlarged nearly triangular anteriorly. Ornamentation consists of 24–29 radial ribs slightly curved towards the anterior. Ribs are a little rounded on internal moulds and faintly flattened on external shell surface. On the surface of the ribs, on older shell portions, there are medium−sized, rounded tubercles as a result of crossing ribs by growth lines. Tubercles disappear at the ventral margin and delicate rounded chevrons replace them. Interspaces are narrower or have the same width as the ribs.

Discussion.—The large ligament area anteriorly suggests this species to belong to the genus Glyptohallicardia . On two specimens, remains of the shell are preserved, but ornamentation is weak and obliterated. Thus the above description is based on internal moulds. Within the population of these bivalves there is no strong differentiation in shell shape, defined by the ratios L/H and W/2/H. The average value of L/H is 1.07, while W/2/H – 0.36 ( Fig. 8 ).

Occurrence.— Known exclusively from the type locality and coeval deposits from Ściegnia section (Łysogóry region; Penczek 1995) .

Figures

Fig. 6. Bivalves from the Early Frasnian Goniatite Level (uppermost Szydłówek Beds) at Kostomłoty and Ściegnia, Holy Cross Mountains, Poland. A–F. Glyptohallicardia multicostata sp. nov. A. Holotype, GIUS 4−2290 Kos−20, in lateral (A1), posterior (A2), ventral (A3), and dorsal (A4) views. B, F. GIUS 4−2291 Kos−21/2 (B) and GIUS 4−2847 Wz−41a/1 (F) in lateral views. C, D. GIUS 4−2291 Kos−21/1 (C) and GIUS 4−2291 Kos−21/8 (D) in posterior views. E. GIUS 4−2291 Kos−21/6 in dorsal view. G–J. Glyptohallicardia aff. G. conversa (Clarke, 1904). G–I. GIUS 4−2577 Kos−44/2 (G), GIUS 4−2577 Kos−44/1 (H), and GIUS 4−2577 Kos−44/4 (I) in lateral views. J. GIUS 4−2577 Kos−44/3 in dorsal view. K. Glyptohallicardia cf. palmata (Goldfuss, 1837), GIUS 4−2296 Kos−26 in lateral view. L.?Metrocardia sp., GIUS 4−2295 Kos−25 in lateral view. M–O. Glyptohallicardia ferruginea (Holzapfel, 1895). M. GIUS 4−2293 Kos−23/1 in lateral view. N. GIUS 4−2293 Kos−23/2 in posterior view. O. GIUS 4−2293 Kos−23/3, fragment of valve with ornamentation visible. P, Q.?Cabricardium sp. P. GIUS 4−2581 Kos−48/1 in lateral view. Q. GIUS 4−2581 Kos−48/2 in lateral (Q1) and dorsal (Q2) views. R. Leptodesma sp., GIUS 4−2297 Kos−27 in lateral view.

Fig. 8. Distributions of ratios L/H (A) and W/2H (B) indexes of Glyptohallicardia multicostata sp. nov. from the Early Frasnian (Szydłówek Beds) at Kostomłoty. Note: some points actually refer to more than one specimen.