Orthambonites sp.
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publication ID |
https://doi.org/ 10.4202/app.2009.0032 |
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persistent identifier |
https://treatment.plazi.org/id/03E4879F-7267-9571-1266-FAB0FEBE3172 |
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treatment provided by |
Felipe |
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scientific name |
Orthambonites sp. |
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Fig. 5 View Fig .
Material.—Five internal moulds and one external mould of ventral valves, and nine internal moulds and four external moulds of dorsal valves, with numbers MGM−5999−O to MGM−6017−O.
Description.—Shell large, up to 26 mm wide and 19 mm long, slightly ventribiconvex, subrectangular in outline, maximum width along hinge line or close to it, depending on growth stage, cardinal angles acute in young stages and slightly obtuse in adults, 79–83% as long as wide, and with slightly sulcate anterior commissure. Ventral valve slightly convex, with weak median fold and almost flat posterolateral areas; ventral interarea apsacline, slightly curved and relatively short, 6–10% as long as valve, with open delthyrium. Dorsal valve slightly convex to subplanar, with shallow median sulcus, 70–89% as long as wide (m = 76%, v = 0.1%, n = 13); dorsal interarea anacline, flat and short, 4–9% as long as valve, with open notothyrium. Radial ornamentation costate with high ribs of rounded section, numbering 24–28 at dorsal valve margin, and 7–10 per 5 mm counted 5 mm anterolaterally from umbo; fila and capillae well marked on ribs and intercostal spaces, with 4 capillae per 1 mm, 6 fila per 1 mm, as well as up to 3 strong growth lines.
Ventral interior with triangular teeth and large crural fossettes, short dental plates diverging onto valve floor, mus−
doi:10.4202/app.2009.0032
cle field of subrhomboidal outline, 32–43% as long as valve, 21–36% as wide as valve, with adductor scar 3–5% as wide as muscle field; mantle canal system saccate, with parallel and adjacent vascula media until anterior third of valve, diverging close to anterior margin.
Dorsal valve with high ridge−like cardinal process, high notothyrial platform, continuous with wide median ridge that extends anteriorly 16–25% of valve length; brachiophores rod−like, strongly divergent, welded to notothyrial platform; dental sockets excavated on secondary shell deposits; muscle field quadripartite, 40–47% as long as valve, 26–33% as wide as valve, with posterior adductor scars of petaloid outline, twice as long as anterior scars, separated by curved transverse ridges, diverging anteriorly.
Ribbing strongly impressed on internal margins of both valves, with wide intercostal spaces divided shallow sulci.
Discussion.—In its profile, outline, ornamentation and arrangement of ventral vascula media, these orthid shells can be ascribed to Orthambonites Pander, 1830 . They are close to Orthambonites majusculus Rubel, 1961 in the similar number of costae and in the subrectangular outline, although that species is more strongly convex. It is also close to Orthambonites ? novitas Öpik, 1939 in the number of ribs, although that species displays some of them as being usually branched. However, the small Iberian sample, in which no specimen preserves both internal and external features, does not allow a specific identification.
Stratigraphic and geographic range.— This species is known from the localities SP−II (San Pablo de los Montes), NE−II (Navas de Estena) and VPA (Ventas con Peña Aguilera), in the lower part of the Navas de Estena Formation, and from CHI−I (Chillón), VM−I (Viso del Marqués) and CC−III−IIIA ( Calzada de Calatrava ), in the lower part of the Río Formation .
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