Argopecten insuetus del Río, 1992
DEL RÍO, C. J. 1992. Middle Miocene bivalves of the Puerto Madryn Formation, Valdes Peninsule, Chubut Province, Argentina (Nuculidae-Pectinidae), Pt. I. Palaeontographica, Palaeontologie A, 225: 1-58, pls. 1-8, 25 text-figs. [p. 44, pl. 7, figs. 3-6]
1992 Argopecten insuetus del Río, 1992
C. J. del Río, 1992, plate 7.
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«Holotype: CPBA 12.958, a right valve from Lobería Punta Pirámide (LPP8), from Puerto Madryn Formation, Middle Miocene (DEL RÍO collection).
Material: Holotype, thirteen right valves and four left valves from Lobería Punta Pirámide (LPP8): CPBA 12.960, CPBA 15.359-15.363; CPBA 15.364 (LPP6); Puerto Pirámide CPBA 11.600; CPBA 11.614-11.619; CPBA 11.642, CPBA 11.645 (PPll); Punta Ninfas (PNI9); CPBA 11.639-11.641; CPBA 11.643-11.644. All material from Puerto Madryn Formation, Middle Miocene (DEL RÍO collection). Derivatio nominis: From the latin insuetus: rare, scarce, for this species is an uncommon taxon in the exposures of Puerto Madryn Formation. Diagnosis: Shell of medium size. Auricular free margins forming right-angle at junctures with the outer ligament. Plicae longitudinally grooved or with a secondary faint riblet. Interspaces bearing a central riblet and conspicuous concentric lamellae. Description: Shell of medium size, thin, slightly inflated, left valve more convex than right valve, as high as long. Dorsal margin of the disk straight. Auricles subequal. Hinge margin long (AL/L X 100 = 62%-77%). Right valve with anterior auricle ornamented with 6 to 8 wide squamous riblets; free margin straight or slightly rounded. Byssal notch wide, with angular apex and straight fasciolar margin. Posterior auricle slightly shorter than anterior, sculptured with 10 to 13 scaly and incipient riblets; free margin forming right-angle at junctures with outer ligament, and slightly sigmoidal at plane of commissure. Resilial pit shallow, triangular equilateral. One or two pairs of prominent cardinal crura. Posterior auricular denticle moderately strong and extended. Ctenolium with 4 pectinidial teeth. Ribbing of the disk consisting of 13 to 17 flattened plicae, subrectangular in cross section, with vertical sides and separated by narrower and flattened interspaces; top of plicae longitudinally grooved or with a faint riblet starting at 40 mm from the umbo and another riblet on each side that appear at 50 mm from beak; interspaces bearing a squamous riblet starting at 15 mm from beak. Concentric sculpture consisting of trend of crowded, fine, sharp lamellae, projecting only in interspaces and on sides of plicae where are distally convex. Disk flanks costate and slightly sloping downward. Left valve auricles ornamented by 10 or 13 very fine riblets. Byssal sinus moderately deep. Plicae narrower than interspaces. Measurements in mm:
Comments: Argopecten insuetus n. sp. is a rare taxon among the pectinids of the Puerto Madryn Formation and it is commonly associated with heterodonts and echinoids.
It is remarkably different from other species of this genus but may be compared with Neogene American species. Argopeeten purpuratus (LAMARCK) (WALLER 1969, p. 48, PI. 7-10; Pliocene-Recent, Eastern Pacific) differs in having a more convex right valve, a shallower byssal notch and wider plicae. Argopecten invalidus (HANNA) (MOORE 1984, p. 37, PI. 10, fig. 5, Pliocene, California) has equiconvex shells with oblique growth and interspaces narrower than plicae and without secondary radial sculpture. Argopecten subdolus HERTLEIN (HERTLEIN & GRANT 1972, p. 201, PI. 30, fig. 7-8; PI. 35, figs. 2, 5, 9; Pliocene, California) is comparable with Argopeeten insuetus n. sp. but it has more inflated valves, concave interspaces that are narrower than ribs and all surfaces of shell covered with fine radial secondary sculpture. Differences among this species and Argopeeten gratus n. sp. have been discussed in the comments of the latter taxon». CLAUDIA JULIA DEL RÍO, 1992
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«Conchilla apenas convexa, equidimensional, con la valva izquierda más convexa
que la derecha. Aurículas subiguales, con escotadura bisal ancha y ápice anguloso. Ornamentación exterior de las valvas dada por 13 a 17 pliegues aplanados, con sección transversal rectangular, con lados verticales, longitudinalmente acanalados o con 3 costülitas secundarias suavemente impresas y cubiertos por lámelas comarginales densamente distribuidas por toda la superficie valvar, las que se proyectan a manera de escamas en los interespacios y sobre los laterales de los pliegues. Distribución: Formación Puerto Madryn aflorante en Lobería Punta Pirámide, Puerto Pirámide y Punta Ninfas.» DEL RÍO, C. J. & S. A. MARTÍNEZ CHIAPPARA. 1998. Clase Bivalvia. In C. J. del Río (Ed.), 1998: Moluscos marinos miocenos de la Argentina y del Uruguay. Anales de la Academia Nacional de Ciencias Exactas, Físicas y Naturales, Buenos Aires, Monografía 15: 96 p., pls. 1-26. [p. 59]
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Argopecten insuetus del Río, 1992; C. J. del Río, C. J. & S. A. Martínez Chiappara. 1998, Moluscos marinos miocenos de la Argentina y del Uruguay: Clase Bivalvia, plate 4, figures 4, 5.
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