Ptychonema Perner, 1903

Popov, Leonid E., Ebbestad, Jan Ove R., Mambetov, Amanbek & Apayarov, Farid Kh., 2007, A low diversity shallow water lingulid brachiopod-gastropod association from the Upper Ordovician of Kyrgyz Range, Acta Palaeontologica Polonica 52 (1), pp. 27-40 : 32

Genus Ptychonema Perner, 1903

Type species: Ptychonema nigrum Barrande in Perner, 1903: pl. 57: 16–19 and their figure caption; by monotypy. Middle Ordovician (Beroun) Zahořany Formation at Praha−Strašnice, Barrandian Area, Bohemia, Czech Republic .

Remarks.— Knight (1941) placed Ptychonema with some doubt in the synonomy of Lophospira Whitfield, 1886 . The circumstances surrounding this decision are well explained by Knight (1941) and Horný (1997), and will not be repeated here. However, following studies of topotype material and similar specimens from the Anti−Atlas of Morocco, Horný (1997) was able to confidently re−establish the genus. Species of the genus are typically widely spread in the Early Palaeozoic Mediterranean Province, mainly from the Bohemian part of the Czech Republic, Armorica ( Spain, Portugal, and France), and Anti−Atlas, Morocco (see Horný 1997 for references). Commonly, several tens to hundreds of specimens may occur on bedding planes or in nodules, though preservation is highly variable (Radvan J. Horný, personal communication 2005).

Four species are known from the Mediterranean Province: Ptychonema nigrum from the Zahořany Formation (Caradocian) in the Barrandian area, Czech Republic; P. bussacense ( Sharpe, 1853) from the Llanvirnian to Dobrotiva (Darriwilian) of Portugal, Spain, and France (see Horný 1997: 55 and references); P. desideratum (Barrande in Perner, 1903) from the Llanvirnian Šárka Formation and the Dobrotivá Formation (Dobrotiva) in the Barrandian area, Czech Republic; P. marocanum Horný, 1997 , from the Tachilla Formation (Llanvirnian), Anti−Atlas, Morocco. Horný (1997) considered that P. desideratum may be a junior synonym of P. bussacense , but lacked access to type and comparative material for a detailed study.

Abundant specimens of Sinuopea ? sp. were recorded from the shallow water deposits of the Reedsville Formation (Cincinnatian), central Appalachians ( Bretsky 1970). The species is large, 35 mm high, with at least five whorls of uniform expansion rate. A distinct U−shaped sinus is developed with its deepest part (ab−aperturally) at the periphery of the evenly rounded whorl. These features seem to place the taxon with Ptychonema as currently understood, to which it is here transferred. Museum material of this species at the Yale Peabody Museum has not been studied, so details of the aperture morphology and early whorls are unknown. Both in size and morphology the species is comparable to the type species P. nigrum , though the American form is much younger. Inclusion of the species from Kyrgyz Range, described here from the Almaly Formation (Caradocian) in the western Kyrgyz Range, provides the second occurrence of Ptychonema outside the Mediterranean Province.

Perner (1903) described several Silurian Gondwana genera (i.e., Horiostomella , Sellinema , Turbomaria ) with shallow U−shaped sinuses. These were considered junior synonyms of Umbospira Perner, 1903 by Wagner (2002) and placed in the Holopeidae . The affinity of these dominantly Silurian forms with Ptychonema is unclear and remains to be studied (Radvan J. Horný, personal communication 2005), and any Ordovician occurrences should be scrutinized in the light of the resurrection of Ptychonema . For instance, a common, minute species of Turbomaria was reported from the Late Ordovician Boda Limestone of Sweden ( Gubanov et al. 1999). This has an anomphalous shell of four whorls, steep and weakly convex whorl profile with the periphery positioned low on the whorl, and a shallowly convex base. A shallow U−shaped sinus is placed somewhat above the periphery of the whorl. Other Ordovician occurrences of Turbomaria have not been reported, but Sellinema ? sp. was identified from the Late Ordovician on Read Island, Canadian Arctic ( Miller and Youngquist 1947). This species is comparable in size and age with the Cincinnatian Ptychonema sp. , and was described as having a rounded sinus. Type material in the Yale Peabody Museum has not been investigated, so affinities with respect to Ptychonema or the predominantly Silurian Umbospira (synonym Sellinema ) remain open. Furthermore, Horný (1997) predicted that several Ordovician species allied with Mourlonia de Koninck, 1883 may belong to Ptychonema . However, as presently understood, Ptychonema is restricted to the six Ordovician species noted above.