Weyla (Lywea) unca (R. A. Philippi, 1899)
PHILIPPI, R. A. 1899. Los fósiles secundarios de Chile. Primera Parte. 104 p., pls. 1-42. Santiago de Chile. [p. 30, pl. 17, fig. 3]
R. A. Philippi, 1899, plate 17.
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«Pecten ovatus, obliquus, costis 13-14 actiusculis ornatus; valva superiore convexa, costis angustis; valva inferiore valde convexa, costis angustis, modice prominentibus, apicibus valde involutis, uncinatis; auriculis.... — Altit. usque ad 72 mm. et forte uiajor. longit. totidem, crassit. forte 52 mm.
Amolanas in prov. Atacama. Communicavit Grust. Ad. Flühmann.
La concha es aovada oblicua, adornada de 18-14 costillas algo agudas; la valva superior es convexa i sus costillas angostas; la inferior es mui convexa, i sus costillas angostas no sobresalen mucho; los vértices son mui arrollados, como ganchos. He reproducido en la figura el mejor ejemplar, en el cual ambas valvas están juntas, pero las orejuelas faltan, i la parte entre los vértices está tapada con roca. Esta especie es mui notable por sus vértices arrollados i su valva superior convexa.» RUDOLPH AMANDUS PHILIPPI, 1899
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«Description: In contrast to other species of Weyla described above, Weyla (Lywea) unca is biconvex at all ontogenetic stages. The right valve is more convex than the left valve. The right valve is higher than long, whereas the left one is longer than high.
The ribs, 12 to 13 in number, and the interspaces are V-shaped in cross section on both valves. They decrease in strength toward the ventral margin. The interspaces are of the same width as the ribs. On the flanks of the ribs, a fine radial striation and subtle growth lines can be seen. Remarks: W. unca is the only species of Weyla described here that is biconvex. The specimens figured by Damborenea (1987b) as Weyla (Lywea) meeki are considered to belong to W. unca (see Aberhan, 1998a, p. 122). W. meeki (proposed by Damborenea, 1987b, to replace Pecten acutiplicatus Meek) has a plano-convex shell (Aberhan 1998a) and possibly is another junior synonym of W. alata (see above). This is the first record of this species from the Lower Jurassic of Mexico.» SCHOLZ, A., M. ABERHAN & C. M. GONZÁLEZ-LEÓN. 2008. Early Jurassic bivalves of the Antimonio terrane (Sonora, NW Mexico): Taxonomy, biogeography, and paleogeographic implications. Geological Society of America, Special Papers, 442: 269-312, figs. 1-17. [p. 288, 290]
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Weyla (Lywea) unca (Philippi, 1899); A. Scholz, M. Aberhan & C. M. González-León, 2008, Early Jurassic bivalves of the Antimonio terrane, figures 10A, 10B.
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«Affinities: This species differs from all Weyla s. s. species by its globose left valve, the auricles not separated from the disc by a furrow and the absence of a byssal sinus.
The ornamentation of the right valve is similar to that observed in Weyla almelae QUINTERO & DE LA REVILLA (1966: 41, lam. 5, fig. 1a-b), from the Lower Jurassic of Spain, which can be distinguished by having only six radial ribs. The left valve of the Spanish species is unknown. Weyla pradoana (VERN. & COLL.), from the Lower Jurassic of Guadalajara, Spain (DE VERNEUIL & COLLOMB 1853: 163, pl. 3, fig. 4), to which some South American specimens were referred (see below), is smaller, has more pointed auricles, a byssal sinus and a flat left valve, at least on some specimens. A detailed study of this species will probably reveal its affinities to Weyla ambongoensis (THEV.) from Africa and Asia. According to MEEK'S original description (1864: 46, pl. 8, fig. 3) W. meeki new name (= Pecten acutiplicatus MEEK, 1864 non P. acuteplicatus ALTH 1850) shares the V-shaped ribs with W. unca, but has two radial ribs on one of the auricles and between 14 and 15 radial ribs on the disc. These features are not shown, however, in the specimens referred to W. acutiplicata and housed at the BMNH (L 70795 and L 70798), see text-fig. 26, which only differ from W. unca in the ribbing pattern of the left valve, lacking more prominent ribs. Pecten Iycorrhynchus R. PHILIPPI (1899) is probably a synonym of W. unca, but even in that case the name unca is preferred because it was introduced for better preserved material and was later used by several authors. Remarks: Since the end of the last century the presence of "Pecten pradoanus" has been repeatedly mentioned for the lower Jurassic of Argentina. Several of these records were here considered as belonging to W. unca, on the basis of the observation of material from the same localities. Thus, at least part of the material described as "Pecten pradoanus" by BEHRENDSEN (1891, 1922, Taf. 22, fig. 1d) may belong to this species. WEAVER (1931) suggested that it was a young shell of W. alata and in fact, the specimen in BEHRENDSEN'S figure 1a-b may be a juvenile of other Weyla species, as it can be distinguished from W. unca by the presence of radial ribs on the internal mould of the right valve.
The specimens referred to W. pradoana by JAWORSKI (1914a), GERTH (1925) STEINMANN (1929) and WEAVER (1931), certainly belong to the new subgenus, but their specific determination is not easy as they apparently lack the differently prominent left valve ribs. On the other hand the material figured by RANGEL (1978) from the lower Jurassic of Peru, shows the typical unequally strong ribs on the left valve and almost certainly belongs to W. unca. W. pradoana is therefore thought to be absent from South America. This is a very poorly known species and its affinities with either Weyla s. s. or Weyla (Lywea) cannot be established yet. It must be pointed out, nevertheless, that the unequally strong radial ribs of the left valve, though a typical character for this species, are not always evident, especially on poorly preserved or weathered specimens, and are not evident on the inner moulds, which are almost smooth.» DAMBORENEA, S. E. 1987. Early Jurassic Bivalvia of Argentina; Part 2, Superfamilies Pteriacea, Buchiacea and part of Pectinacea. Palaeontographica, Abteilung, A, Palaeozoologie-Stratigraphie, 199 (4-6): 113-216, pls. 1-14. [p. 189]
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Weyla (Lywea) unca (R. Philippi); S. E. Damborenea, 1987, Early Jurassic Bivalvia of Argentina, Part 2, Superfamilies Pteriacea, Buchiacea and part of Pectinacea. plate 12, figure 4; plate 13, figures 1-11.
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