Argopecten eccentricus eccentricus (Gabb, 1873)
GABB, W. M. 1873. On the topography and geology of Santo Domingo. American Philosophical Society Transactions, n. s., 15: 49-259. [p. 256]
1873 Pecten eccentricus Gabb, 1873
Argopecten eccentricus eccentricus (Gabb, 1873); T. R. Waller, 2011, Neogene Paleontology of the Northern Dominican Republic, plate 4, figures 11-14.
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«Shell slightly inequivalve, oblique, ears small, surface covered with twenty-two flat ribs, sometimes slightly grooved, and with concave interspaces. Diameter 1 to 1.5 inch.
Nearest to P. irradians, Lam., but more oblique, and with broader, flatter ribs». WILLIAM MORE GABB, 1873
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«Comparisons.— Argopecten eccentricus eccentricus differs from A. e. lacabrensis n. ssp. in having nearly equiconvex rather than distinctly left-convex valves in early ontogeny, auricles of more equal length rather than with the right anterior auricle noticeably longer than the posterior auricles, less deeply sinuate posterior auricular margins that meet the dorsal margins at more obtuse angles, and earlier fade-out of dorsal costae on the right posterior auricle. Compared to A. e. caimiticus, A. e. eccentricus is less gibbous, with narrower ribs on the right valve that are trapezoidal rather than rectangular and frequently have grooved crests, and with ribs of the left valve frequently with flattened rib crests rather than sharply rounded and somewhat rugose crests.
Brown & Pilsbry (1911: 365) thought that Pecten operculariformis Toula, 1909, based on a single right valve from the Gatun Formation of Panama, is closely related to Argopecten eccentricus s. l. from the Dominican Republic. This relationship is not at all indicated by Toula's figure (1909: pl. 26, fig. 3), which shows that his species is in the genus Euvola. Argopecten eccentricus eccentricus closely resembles the extant Caribbean A. nucleus in shape, ribbing, and size of auricles in relationship to disk, but the latter differs in being more gibbous and in having prominent radial costae on its disk flanks forming a transition in amplitude between disk ribs and auricular costae. Evolution.— Argopecten eccentricus s. l. of the northern Dominican Republic is a species lineage with substantial morphological variation within and among samples. The species is subdivided here into three successive chronological subspecies: A. e. lacabrensis n. ssp., A. e. eccentricus, and A. e. caimiticus. These subspecies are interpreted to be evolutionary stages of a single lineage, because (a) they occur in stratigraphic sequence without apparent reversals, (b) they are connected by transitional forms within the stratigraphic intervals that separate the subspecies, and (c) morphological changes within each of the first two subspecies also occur in stratigraphic sequence. That these subspecies are not merely ecophenotypes resulting from increasing depths of deposition within the measured river sections is suggested by the fact that all three subspecies occur in shallow-water facies. This facies appears to represent a fairly uniform, seagras-supporting, shallow-water marine paleoenvironment as indicated by other fossils, including benthic foraminiferans, gastropods, and other bivalves (see section on Paleoecology). The biostratigraphic implications of the distributions of these subspecies within the Cibao Valley are discussed in the section on Biostratigraphy at the beginning of this monograph. Occurrence.— Argopecten eccentricus eccentricus occurs in the upper Cercado and lowermost Gurabo formations, of Late Miocene age (Table 7). Distribution.— The presence of Argopecten eccentricus eccentricus outside of the Dominican Republic has not yet been substantiated». WALLER, T. R. 2011. Neogene Paleontology of the Northern Dominican Republic. 24. Propeamussiidae and Pectinidae (Mollusca: Bivalvia: Pectinoidea) of the Cibao Valley. Bulletins of American Paleontology, 381: 1-197. [p. 49]
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Argopecten eccentricus eccentricus (Gabb, 1873); T. R. Waller, 2011, Neogene Paleontology of the Northern Dominican Republic, plate 5, figures 1-5.
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«Shell with a general resemblance to P. irradians Lamarck, but with broader, flatter ribs numbering twenty to twenty-two, sometimes feebly grooved medially; interspaces concave; ribs and interspaces with looped growth lines; ears small. Length of our largest shell 38, altitude 35, semidiameter 11 mm. Gabb gives 2 5 to 38 for the length of the types.
Our shells appear to be this unfigured species as they accord with Gabb's description. Localities.— (Exp'd '16) Bluffs 1, 2 and 3, Cercado de Mao.» MAURY, C. J. 1917. Santo Domingo Type Sections and Fossils. Part 1: Mollusca. Bulletins of American Paleontology, 5 (29): 166-415, pls. 1-39. [p. 351]
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Pecten excentricus Gabb; C. J. Maury, 1917, Santo Domingo Type Sections and Fossils, plate 34, figure 8.
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