Schellwienella ornata Demanet, 1934

Mottequin, Bernard & Simon, Eric, 2017, New insights on Tournaisian-Visean (Carboniferous, Mississippian) athyridide, orthotetide, rhynchonellide, and strophomenide brachiopods from southern Belgium, Palaeontologia Electronica 37 (3), pp. 1-45 : 19-21

Schellwienella ornata Demanet, 1934

Figures 4 , 15

v* 1934 Schellwienella ornata nov. sp. Demanet, p. 83, text-fig. 16, pl. 7, figs. 4-5.

Type material. The complete internal mould ( RBINS a5922) illustrated by Demanet (1934, pl. 7, fig. 4) is selected herein as the lectotype ( Figure 15.1-8 ) whereas the specimen ( RBINS a5923) figured by Demanet (1934, pl. 7, fig. 5, text-fig. 16) and of which the ventral umbo has been sectioned by him, is selected as the paralectotype ( Figure 15.9-14 ). Both specimens were considered as paratypes by Demanet (1934). Until now, although Demanet (1934, p. 84) reported other specimens assigned to his new species, only the types have been recovered.

Description. Shell medium-sized (up to 41.8 mm in width), markedly ventribiconvex, subquadrate in outline, with maximum width near midlength; hinge line clearly shorter than maximum width; cardinal margins rounded; anterior margin straight or depressed; anterior margin rectimarginate or vaguely undulose.

Ventral valve moderately inflated, with flanks sloping moderately towards lateral commissure; umbo not prominent (at least in internal mould) beak straight; interarea irregularly triangular (deformation due to cementation on an organic or inorganic substrate), high, flat, apsacline; perideltidium flat; pseudodeltidium narrow, strongly convex; cementation cicatrix only preserved in lectotype.

Dorsal valve slightly convex, with maximum height near mid-valve then slightly decreasing towards anterior margin; interarea linear, flat, anacline; shallow median depression originating near posterior margin developed in one specimen.

Ornamentation parvicostellate ( Figure 15.14 ); costellae increasing by intercalation, 6–7 costae per 5 mm near front separated from each other 5–6 costellae; growth varices developed; filae absent.

Ventral interior ( Figure 15.1-2 , 5 , 7 ) with thin dental plates diverging at an angle of 35–37 degrees; teeth small; muscle field not excavated, obscure.

Dorsal interior ( Figure 15.3 , 7-8 ) with posteriorly grooved cardinal process lobes; socket ridges recurved, widely divergent; muscle field slightly excavated, obscure but well-defined posteriorly by lateral ridges extending from the socket ridges.

Remarks. Despite the availability of the type material illustrated by Demanet (1934), Schellwienella ornata remains incompletely known as its intraspecific variability cannot be investigated. Its main features are the parvicostellate ornamentation devoid of filae and the slightly divergent dental plates, which are not without evocating the genus Pulsia Ivanov, 1925 , but the latter is characterized by parallel dental plates whereas Schellwienella encompasses species with dental plates variably divergent from hinge line ( McIntosh, 1974). Schellwienella ornata differs from S. crenistria ( Phillips, 1836) by the absence of filae, its quadro-rounded outline, and its narrow hinge line (the maximum width is near midlength vs. close to the hinge). According to Demanet (1934), his species is very similar to Orthis cylindrica M’Coy, 1844 from the Visean (Brigantian) of Castle Espie (Comber, Co. Down, Ireland). M’Coy’s (1844, pl. 22, fig. 1) original specimen was illustrated by Davidson (1861, pl. 27, fig. 9), and this species was considered as probable Schellwienella representative by Thomas (1910, p. 127). Furthermore, Orthis cylindrica was considered as a variety of Schellwienella crenistria ( Phillips, 1836) by Davidson (1861, p. 128; 1880, p. 290). Note that the specimens from the Serpukhovian of Scotland (base of the Millstone Grit Series) identified as Streptorhynchus crenistria var. cylindrica M‘Coy and illustrated by Davidson (1880: pl. 37, figs. 6–7) have been assigned to Schellwienella rotundata Thomas, 1910 and Orthothetina cf. thomasi (Sokolskaya in Sarytcheva and Sokolskaya, 1952) by McIntosh (1974: 204, 209), respectively. The only specimen illustrated by M‘Coy (1844) cannot be found in the Griffith collections curated at the National Museum of Ireland, but there is a dorsal valve (NMING:F6267) ( Figure 16 ) from the same locality which matches M’Coy’s description; thus it is herein selected as lectotype for nomenclatorial purposes. The type specimens of Demanet’s (1934) species have a markedly less convex dorsal valve and a thinner radial ornamentation. Thomas (1971) noted the similarities between the ornamentation of S. ornata and those of S. reprinki Sokolskaya (in Sarytcheva and Sokolskaya, 1952) (see also Sokolskaya, 1954) and S. weaberensis Thomas, 1971 .

Occurrence. The type specimens were recovered from the Visé Formation at Visé according to Demanet (1934), who also reported the species in the ‘calcschistes de Warnant’ in the Condroz sedimentation area, corresponding now to the Upper Member of the Anhée Formation (see Poty et al., 2002) (late Warnantian; Figure 4 ). However, Demanet (1958) did not report this species anymore within the Anhée Formation.

Figures

FIGURE 4. Distribution of the athyridides, orthotetides and strophomenides described and/or discussed herein within the essentially carbonate Tournaisian and Visean succession of southern Belgium (see text). Stratigraphy, lithostratigraphy (incompletely represented here for the Hainaut and Visé–Maastricht sedimentation areas; formations and members are in roman and italic letters, respectively), and biostratigraphy are adapted from Poty et al. (2002, 2006, 2014). The lenticular Vignobles Member is not represented here as it is rarely developed (it is comprised between the Vaulx Member of the Tournai Formation and the Antoing Formation). Note that the “Grande Brèche” is an informal stratigraphic unit resulting from the dissolution of evaporitic levels in the Grands Malades Formation; other brecciated horizons occur in the Lives Formation.

FIGURE 5. Leptagonia franca sp. nov. from the Tournai area, Tournai Formation (Tournaisian). 1-6, RBINS a5891 (holotype), articulated specimen, almost complete, in ventral (perpendicular to the surface of the alae), dorsal, lateral, posterior, anterior, and ventral (perpendicular to the disc) views. 7-12, RBINS a5892, articulated specimen, almost complete, in ventral (perpendicular to the surface of the alae), dorsal, lateral, posterior, anterior, and ventral (perpendicular to the disc) views. 13-18, RBINS a13099, articulated specimen (with an auloporid tabulate fixed to its right ventral flank), almost complete, in ventral (perpendicular to the surface of the alae), dorsal, lateral, posterior, anterior, and ventral (perpendicular to the disc) views. Scale bar equals 10 mm.

FIGURE 7. Leptagonia franca sp. nov. from the Tournai area, Tournai Formation (Tournaisian). 1-3, Detail of the small pseudodeltidium and apical foramen of three articulated specimens with the ventral valve on top: RBINS a5896 (1), RBINS a13103 (2), and RBINS a5895 (3). 4-5, RBINS a5902, incomplete ventral valve showing the posterior morphology. 6-7, RBINS a a13104, incomplete ventral valve interior showing the posterior morphology and posterior view notably displaying the prominent teeth. 8, RBINS a5903, incomplete ventral valve interior showing the posterior morphology. 9, RBINS a5899, almost complete dorsal valve interior in ventral view. 10-13, RBINS a5897, almost complete dorsal valve interior in posterior and ventral views, detail of the lateral vascular canals, and close-up of the cardinal process and the muscular field. Scale bars equal 2.5 mm (1-3), 5 mm (4-8, 12-13), 10 mm (9-11).

FIGURE 15. Schellwienella ornata Demanet, 1934 from Visé, Visé Formation (Visean, Warnantian). 1-8, RBINS a5922 (lectotype), articulated internal mould in ventral, enlarged ventral (showing the extent of the traces left by the dissolved dental plates), dorsal, lateral, posterior, and anterior views, and internal views of a latex cast (SEM) showing the internal morphology of the posterior part of the specimen (7-8). 9-14, RBINS a5923 (paralectotype), articulated specimen (partly sectioned, probably by Demanet) in ventral, dorsal, lateral, posterior, and anterior views, and close-up (SEM) of the parvicostellate ornamentation in the central part of the dorsal valve. Scale bars equal 10 mm (1, 3-6, 9-13), 5 mm (2), 2.5 mm (7-8), 1.25 mm (14).

FIGURE 16. Schellwienella cylindrica (M’Coy, 1844), from the Visean (Brigantian) of Castle Espie (Comber, Co. Down, Ireland). 1-3, NMING:F6267 (lectotype), almost complete dorsal valve in dorsal, lateral, and posterior views. Scale bar equals 10 mm.