Amusium aguaclarense (F. & H. Hodson, 1927)
HODSON, F., H. K. HODSON & G. D. HARRIS. 1927. Some Venezuelan, and Caribbean mollusks. Bulletins of American Paleontology, 13 (49): 1-80, pls. 1-40. [p. 36, pl. 18, fig. 1; pl. 21, figs. 1, 2]
1927 Pecten (Amusium) aguaclarensis F. & H. Hodson in Hodson et al., 1927
F. Hodson, H. K. Hodson & G. D. Harris, 1927, plates 18, 21.
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«Shell averages 85-100 mm. in altitude, and is about as long as high. Both valves are moderately convex with in conspicuous, concentric lines of growth. In well preserved fragments, the internal lirae are visible on the outside of the shell as dark, radial lines. The specimens are frequently very much thickened with gypsum; in some cases, the replaced shell is 10-15 mm. thick, instead of less than 1 mm., which is its normal thickness. The right valve is strengthened with about 10 pairs of internal lirae; the distance between each pair is 2-4 times as great as the interval between the constituent lirae. The left valve has 10-12 pairs of internal lirae; the distance between the pairs is about equal to or slightly greater than the distance between the lirae which constitute a pair. In both valves, the submargins are fairly wide. Specimens of either valve may occasionally show supplementary lirae adjacent to, and parallel to, the main pairs of lirae.
This character of having equally spaced lirae in one valve and paired lirae in the other valve is found in P. pleuronectes Linné, which is slightly larger and does not have such prominent liiae in the younger stages. Age: Oligocene-Miocene. Locality: Districts of Federación, Buchivacoa, Democracia and Miranda, State of Falcón ; District of Urdaneta, State of Lara; locality numbers 15, 16, 806, 810, 995, 1058, 1129, 1264, 1287, 1290, 1291, 1294, 1733, 1735, 1736, 1737, 1740, 1939, 1979, 2035.» FLOYD HODSON & HELEN K. HODSON, 1927
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«Based on a new examination of specimens from Panama studied by Woodring (1982), the species that he described as Amusium toulae from the La Boca, Alhajuela, Gatun, and Chagres formations of Panama is actually two species. One is restricted to the La Boca Formation and is identified herein as A. aguaclarense (F. & H. Hodson in Hodson et al., 1927). The latter species was described from the Agua Clara Formation of Venezuela, a stratigraphic unit that is apparently of approximately the same age as the La Boca Formation (late Early Miocene, Burdigalian). The second species included within "A. toulae" by Woodring is the true A. toulae, which does not occur in the La Boca Formation but is present in the Alhajuela, Gatun, and Chagres formations.
Morphotypes A and B of Amusium papyraceum differ from A. aguaclarense, A. toulae, and A. mortoni in the shape of the free margins of the auricles and in the extent of foliated-calcite re-entry on the shell interior. In the latter three species, the dorsal part of the free margins of the auricles sweep dorsally toward the beak to form a more obtuse angle with the dorsal margin than in A. papyraceum. In Panamanian A. aguaclarense, A. toulae, and A. mortoni, the inner aragonitic sector is broader than in A. papyraceum, so that the posterior margin of the adductor scar of both valves is inset from the aragonite margin posterior to the scar, whereas in A. papyraceum the posterior margin of the adductor scar is flush with the margin of the aragonite sector. Also, A. papyraceum differs from these other species in having more extensive foliated-calcite re-entries, extending to below the level of the ventral margin of the adductor scar in mature specimens, whereas in the other species, this shell layer barely extends to the mid-adductorscar level. Amusium aguaclarense differs from all of the other species in the number and pattern of its internal carinae. Its right valve commonly has 8-10 broad pairs of carinae, with interpair spaces not more than approximately twice the width of intrapair spaces. Because the carinae of the left valve are on the outer sides of the paired carinae of the right valve, interand intrapair spaces of the left valve are the same width or nearly so, making pairs impossible to distinguish. The number of single carinae on the left valve of A. aguaclarense (16-20) is therefore twice the number of pairs on the right valve. Amusium mortoni differs from the other species in attaining a much greater maximum size (heights commonly > 100 mm, rarely exceeding 200 mm) and in having obsolete disk flanks on the left valve so that the auricular surface and adjacent disk surface are at the same level, separated only by a groove.» 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, pls. 1-18. [p. 98, 99]
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Amusium toulae (Brown & Pilsbry), La Boca Formation; W. P. Woodring, 1982, Geology and paleontology of Canal Zone and adjoining parts of Panama, plate 96, figures 5, 7, 8; plate 100, figure 10.
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