Amusium paris 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. [p. 23, pl. 2, figs. 3-4; pl. 3, figs. 1-2]
1992 Amusium paris del Río, 1992
C. J. del Río, 1992, plates 2, 3.
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«Holotype: CPBA 15.275 a right valve from Eje Tentativo (ET6), from Puerto Madryn Formation, Middle Miocene (on RÍO collection).
MateriaI: Holotype; eighty seven left valves, eighty nine right valves, two articulated specimens from: Eje Tentativo CPBA 13.561-13.570, CPBA 15.239-15.294 (ET6); Punta Paardela, CPBA 11.619-11.620, CPBA 15.283-15.284 (Pa1); Punta Pirámide CPBA 7837 (thiny four specimens), CPBA 9315 (seventeen specimens), CPBA 15.234-15.238, CPBA 11.586-11.591 (PP5); Lobería Punta Pirámide: CPBA 15.297-15.298 (LPP1); 15.299-15.303, CPBA 13.423 (LPP6); CPBA 15.304-15.321 (LPP8): Ea. El Fracasso (Puerto San José Oeste), CPBA 15.343-15.350 (SJO8); Salina Grande CPBA 15.351-15.353; Fondeadero Ninfas, CPBA 15.354-15.358 (F9). All material from Puerto Madryn Formation, Middle Miocene (DEL RÍO collection). Derivatio nominis: From the latin paris: pair, for the development of radial paired lirae in the interior of both valves. Diagnosis: Shell thin and large in size, attaining heights of 100 mm. Dorsal margin short. Interior sculpture of both valves consisting of 19 to 22 pairs of radial ribs. Description: Shell large in size, thin, equiconvex, a little inflated, equilateral and as high as long. Apical angle obtuse (120º-140º). Disks flanks straight. Auricular margin short, length 33 to 38% of total length of disk. Auricular and dorsal gapes. Auricles equal in size and small. Free margin of anterior right auricle sigmoidal in plane of commissure, with a relict of byssal notch. Free margins of right posterior auricle and of both auricles of left valve straight and forming obtuse angles at junctures with outer ligament. Resilial insertions small, shallow and generally higher than long. A pair of strong auricular crura with prominent denticles in each valve, those in right valve stronger. Cardinal crura short and feebly impressed. Disk and auricle surfaces covered with growth lines, sharper and crowded towards ventral margin. Interior of both valves with 19 to 22 pairs of fine and rounded ribs, more flattened towards the middle region of shell and extending about 50 mm from ventral margin to umbonal area in mature specimens. Measurements in mm:
Comments: Amusium paris n. sp. is a common species throughout the area of exposure of the Puerto Madryn Formation beds and is particularly abundant at Eje Tentativo where different strata yield numerous large and monospecific samples of well preserved, complete and usually articulated valves that are commonly associated with Aequipecten paranensis (D'ORBIGNY) and the braquiopod Pachymagas sp. It is also exceptionally abundant at Lobería Punta Pirámide where it is represented by fragmentary and desarticulated, sometimes complete and articulated specimens, associated with the "giant" pectinids Chesapecten crassus n. sp. and Flabellipecten piramidesensis (IHERING), and with Aequipecten paranensis (D'ORBIGNY).
SOWERBY (1846), IHERING (1907) and subsequent authors (FRENGUELLI 1926, ROVERETO 1921, FERUGLIO 1949) identified this species with Amusium darwinianum (D'ORBIGNY) that occurs in the Miocene Paraná Formation (Entre Rios Province) and was first described and illustrated by PHILIPPI (1893, p. 12, Lám 3, fig. 4). After examining material from the Puerto Madryn and Paraná Formations strata and from lHERING's collection, it is concluded that specimens found on the Valdés Peninsula and in the Puerto Madryn area must be referred to a new species: Amusium paris n. sp. Amusium darwinianum (D'ORBIGNY) is closely related to A. paris n. sp., but the former differs in being thicker, in having longer and higher auricles, a deep, broad and higher resilial pit and 6 to 7 unpaired and equidistant interior lirae situated in the middle ventral region and 6 to 7 pairs of ribs in the anterior and posterior portions of the ventral region. On the basis of external features, A. paris n. sp. is rather similar to both Miocene giant Caribbean and European species buy these taxa are distinguished by fewer internal lirae, usually unpaired on both valves or at least on only one of them, and only occasionally paired lirae on both valves. A. tuolae [sic] (BROWN & PILSBRY) (WOODRING 1982, p. 588. PI. 96, figs. 5, 7, 8) from the Miocene of Venezuela and Panama, differs in having only 8 to 10, exceptionally 14 to 15 right valve paired of internallirae and 16 to 19 equidistant or 14 to 18 paired lirae on left valve. A.lompocensis (ARNOLD) (MOORE 1984, p. 66, PI. 2, figs. 10-11) from the Miocene of California has 14 paired and wider separated lirae on both valves. A. cristatum badenense FONNANNES [sic] (DEPERET & ROMAN 1928, PI. 25, figs. 1-5) from the Miocene of Europe is distinguished by the presence of 22 to 32 single left lirae and 14 to 16 paired lirae on right valve.» CLAUDIA JULIA DEL RÍO, 1992
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«Conchilla delgada con aurículas iguales y pequeñas. Ambas valvas con un par de cruras auriculares fuertemente marcadas y con dentilios prominentes; cruras cardinales cortas y débiles. Interior de las valvas recorrido por 19 a 22 pares de costillas radiales finas y redondeadas.
Distribución: Formación Puerto Madryn aflorante en Eje Tentativo, Punta Pardela, Puerto Pirámide, Lobería Punta Pirámide, Puerto San José Oeste, Puerto San José Este, Salina Grande, Fondeadero Ninfas, Punta Quiroga, Punta Delgada, Lote 39 Cueva Los Leones y Puerto Lobos.; niveles "entrerrienses" presente en las perforaciones Riachuelo 5: 93,60 m - 95,00 m y Riachuelo 4.» 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. 57]
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Amusium parís 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 8, figures 1, 12.
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