Almadenorthis auriculata Reyes−Abril and Villas, 2010

Reyes-Abril, Jaime, Villas, Enrique & Gutiérrez-Marco, Juan Carlos, 2010, Orthid brachiopods from the Middle Ordovician of the Central Iberian Zone, Spain, Acta Palaeontologica Polonica 55 (2), pp. 285-308 : 288-290

Almadenorthis auriculata Reyes−Abril and Villas sp. nov.

Fig. 3.

Etymology: For its auriculate cardinal extremities.

Type material: Holotype: MGM−5940−O, internal and external moulds of ventral valve. Paratypes: three internal moulds of ventral valves, one internal and external mould of ventral valve, and two internal and external moulds of dorsal valves, with numbers:MGM−5941−O to MGM−5945−O, from the lower horizons of the Río Shales .

Type locality: AC−I, 5800 m SE of Fontanosas , but within the municipality of Almodóvar del Campo, Ciudad Real Province, Spain. UTM coordinates: lat 38 ° 44'02''N , long 4 ° 29'34''W.

Type horizon: Lower part of the Río Formation , Didymograptus artus Biozone , lower Oretanian , middle Darriwilian Stage of the Middle Ordovician Series .

Diagnosis.—Shell planoconvex, with transversally elongate semioval and auriculate outline, acute ears in young stages to rounded ears in adult stages; 51–71% as long as wide, with 60% the commonest value. Capillate, filate and coarselly ramicostellate ornament, with 26 to 33 ribs in adults; less than 60% of costae branching. Shell extremely thin, with all radial and concentric ornament strongly impressed on valve interiors.

Description.—Shell planoconvex, up to 15 mm long, very thin, transversely semioval in outline, with variably alate cardinal extremities, from acute ears in young forms to rounded ears in adults (see Fig. 3F 3), 51–58% as long as wide and slightly sulcate to rectimarginate anterior commissure. Ventral valve convex, with low fold, subplanar postero−lateral areas and maximum depth medially, 17–20% as deep as long; ventral interarea apsacline, short, planar to slightly curved, 3–5% as long as valve, with wide and open delthyrium. Dorsal valve planar, with shallow sulcus, progressively widening anteriorly; dorsal interarea anacline, planar, 2% as long

Fig. 3. Orthid brachiopod Almadenorthis auriculata Reyes−Abril and Villas gen. et sp. nov. A. Holotype, MGM−5940−O, internal mould (A 1), latex cast of H interior (A 2) and latex cast of exterior (A 3) of ventral valve. B. MGM−5943−O, internal mould (B 1) and latex cast of interior (B 2) of ventral valve. C. MGM−5941−O, internal mould (C 1) and latex cast of interior (C 2) of ventral valve. D. MGM−5942−O, internal mould (D 1) and latex cast of interior (D 2) of ventral valve. E. MGM−5945−O, internal mould (E 1), latex cast of interior (E 2) and latex cast of exterior (E 3) of dorsal valve. F. MGM−5944−O, internal mould (F 1), latex cast of interior (F 2) and latex cast of exterior (F 3) of dorsal valve. Scale bars 5 mm.

doi:10.4202/app.2009.0032

as valve (measured on one valve), with open notothyrium. Radial ornament coarsely costellate, with ribs branching irregularly; less than 30% of costae branching in young stages, but up to 60% in adults; ribs narrow and high, subrounded in section, numbering 26 to 33 in shell margin, and 7–9 per 5 mm at 5 mm anteromedially from umbo; strongly capillate and filate, with 9–11 fila per mm.

Deltidiodont teeth, with crural fossettes, supported by very short dental plates, divergent toward valve floor; muscle field subtriangular, short, with rounded anterior margin, 22–29% as long as valve, 17–22% as wide as valve, diductor scars nearly as long as subtriangular adductor scar, not enclosing them anteriorly. Two narrow vascula media arise from anterior end of diductors and immediately diverge anteriorly, fading before mid length of valve.

Notothyrial platform short, posteriorly sloping and extending anteriorly as wide median ridge; cardinal process blade−like, high, thickening in adult stages; brachiophores rod−like, welded to nothothyrial platform; dental sockets excavated on valve floor; muscle field poorly impressed.

Shell with even finest radial and concentric ornamentation strongly impressed on interior of both valves (see Fig. 3D 1, E 1). Crenulations (rib reflections) deeply impressed on inner surface of valve margin, narrower than reflactions of interspaces, which lack median sulci typical of many orthid species.

Stratigraphic and geographic range.— Known only from its type locality, AC−I, west of Almodóvar del Campo (Ciudad Real), in the lower horizons of the Río Formation .