Gigadiscina cf. collis ( Clarke, 1913 )

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 cf. collis ( Clarke, 1913)

Fig. 2A .

Material.—Single ventral valve, preserved in ferruginous sandstone of Lower Devonian age, collected between Port Howard and Manybranch Harbour in the Falkland Islands, kept in the Natural History Museum, London (BMNH B 60298).

Description.—The ventral valve is some 60 mm long, flat with a shallow depression around the pedicle foramen. The shell is widest slightly anterior to the midlength. The posterior part of the valve is not preserved, but the courses of the rugellae indicate, that the posterior margin is slightly extended. The surface is ornamented by regular, rather fine and uniform concentric rugellae, numbering 14–15 per 5 mm.

Remarks.—The illustrated herein ventral valve may belong to Orbiculoidea collis Clarke, 1913 or another closely related species, although the holotype of Orbiculoidea collis Clarke, 1913 is known only from a single, dorsal valve ( Reed 1925; Boucot et al. 2001). We found out that our ventral valve shares the same style of sculpture hence can be conspecific. Because the size and morphology of the illustrated herein ventral valve is similar to that of Gigadiscina lessardi sp. nov. we propose to include O. collis to the new genus.

Figures

Fig. 2. A. Gigadiscina cf. collis (Clarke, 1913) from Upper Devonian of Falkland Islands, near Port Howard. External mould of ventral valve, BNMH B 60298. B. Gigadiscina sp. from Middle–Upper Devonian of Libya, Tripoli area (borehole BP, well C1−8). Ventral valve BMHN BD 3385b, external mould (B1), ventral valve BMNH BD 3385a, detail of ornament (B2), detail of microornament (B3), and detail of pitted radial bands alternating with smooth bands (B4).