Amusium rexmaris Maury, 1925
MAURY, C. J. 1925. A further contribution to the Paleontology of Trinidad (Miocene Horizons). Bulletins of American Paleontology, 10 (42): 159-402, pls. 1-43. [p. 242, pl. 15, fig. 1]
«Amusium rex-maris, n. sp. PL 15, Fig. 1
Shell very large, thin, obliquely subcircular, moderately and evenly convex, margins gently curving. Ears rather large, subequal. Exterior surface of shell where perfect showing conspicuous concentric growth lines and occasional ridges of slower growth periods. Interior of shell with paired radial ribs, there being about fourteen pairs. At the basal margin of the valve each pair occupies three to four, and each interspace, eight to fifteen millimeters, the spacing being variable. The ribs appear only on the lower central portion of the interior of the valve, as they become obsolete towards the hinge, and are absent anteriorly and posteriorly. Length of valve 165, altitude 147, approximate semidiameter 18 mm.
The exterior of the beak is concealed by the matrix which is unfortunate, as Dr. Dall has found the umbonal sculpture of the Amusiums valuable in classification. Thus A. mortoni Ravenel, papyraceum Gabb, and luna Brown and Pilsbry, have perfectly smooth beaks, while lyoni Gabb, sol and antiguensis have radial ribs on the exterior of the shell in early stages. On comparing this splendid Amusium with other species having paired internal ribs, it is seen to have fewer pairs. Thus A. mortoni has a minimum of twenty-one, luna and sol have about twenty-three pairs each, and papyracea has them still more closely-set. The largest sol recorded measured 90 x 30 and the largest luna 80 x 76 mm. In size and general aspect our Trinidad Amusium is most like mortoni Ravenel, the very large Miocene to Pliocene species, but has decidedly fewer paired ribs and instead of being nearly circular is so oblique that there is 20 mm. difference in the length of a radial line dropped from the beak to the anterior basal margin from one dropped to the posterior basal margin — the anterior measuring 120 and the posterior 140 mm. Locality.— Springvale. Horizon.— Upper Miocene.» CARLOTTA JOAQUINA MAURY, 1925
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C. J. Maury, 1925, plate 15.
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