Gigadiscina anomala ( Kayser, 1892 )

Mergl, Michal & Massa, Dominique, 2005, A new giant discinoid brachiopod from the Lower Devonian of Algeria, Acta Palaeontologica Polonica 50 (2), pp. 397-402 : 400

Gigadiscina anomala ( Kayser, 1892)

Fig 1F.

Discina anomala n. sp.; Kayser 1892: 96: pl. 10: 1–3.

Holotype: Dorsal valve, internal moulds with remains of original ventral valve, deposited in the palaeontological collection of the Marburg University, Marburg, Germany ( MGB 2107 ).

Type horizon: Devonian, Pragian (Siegenian), Siegenian Greywackes.

Type locality: Germany, Siegen, quarry eastward of Siegen, near “Siegena“ ironworks.

Material.— The holotype, and two complete shells, preserved in sandstone from the quarry east of Siegen , Germany, housed in the Natural History Museum, London ( BMNH B 42906 , BMNH B 42915 ) .

Description.—See Kayser (1892).

Remarks.—The holotype is large, strongly asymmetrical, shell 43 mm long, by 45 mm wide, and 20 mm high. Its ornamentation is preserved only in posterolateral slope, with ten dense rugellae per 5 mm. Two other available complete specimens can be referred to Discina anomala ( Kayser, 1892) . The larger specimen is 60 mm long, with the slightly eccentric dorsal apex, a flat ventral valve with a depression around the pedicle foramen, and distinct concentric rugellae covering shell surface. The second specimen is smaller, with an irregular outline and a flat ventral valve covered by concentric rugellae.

Although closely related, the species Gigadiscina anomala ( Kayser, 1892) differs from G. lessardi sp. nov. by having coarser and more distant concentric rugellae on the shell surface. The larger British specimen ( BMNH B 42906) has the dorsal apex situated posteriorly while the apex of G. lessardi lies anteriorly to midlength. The limited material of G. anomala does not allow us to satisfactorily compare the shell outline but, judging from the drawings of Kayser (1892), the holotype, and two additional specimens, the species G. anomala has slightly more elongate shell.