Amussiopecten harrisi Masuda, 1971
MASUDA, K. 1971. Amussiopecten from North America and Nothern South America. Transactions and Proceedings of the Palaeontological Society of Japan [N. S.], 84: 205-224, pls. 25-26.. [p. 213, pl. 26, figs. 1 a-b]
1971 Amussiopecten harrisi Masuda, 1971
K. Masuda, 1971, plate 26.
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«Holotype:— U.S. Natl. Mus., Coll. No. 646476.
Description:— Shell medium in size, rather thin, compressed, subequivalve; right valve a little more inflated than left valve; valves radiately ribbed and forming an angle of about 110° at apex. Right valve slightly inflated, with about 16 low but rather distinct, perpendicular sided. flatly round-topped radial ribs tending to become obsolete and broad towards ventral and lateral margins, and faint, fine incremental lines; radial ribs broader than their interspaces, which are flatly round bottomed; auricles somewhat angulate, with fine concentric lines and faint, fine radial threads. Left valve slightly inflated, with low, rather flatly rounded radial ribs. which tend to become obsolete towards ventral and lateral margins, crossed by regularly spaced, raised, faint, fine incremental lines; radial ribs nearly equal to their interspaces in breadth at younger stage but tending to become broader than their interspaces with growth; auricles straight, with fine, faint radial threads and concentric lines. Hinge with simple cardinal crura provided with a distinct, fine provinculum, wide and shallow resilial pit, and distinct auricular crura terminating distally in a distinct denticle at each extremity. Interior surface with distinct paired internal ribs near ventral margin. Dimensions (in mm):— Holotype, height 57, thickness 12.5; paratype, right valve, height 28, length 29, depth, ca. 4; right valve, height 45, length 45. Remarks:— This species is named in honor of Late Prof. Gilbert D. HARRIS who greatly contributed to the paleontological studies of Central and South America and founded the Paleontological Research Institution in Ithaca, New York. Comparison:— Amussiopecten vanvlecki can be distinguished from the present new species by its larger shell, nearly flat left valve in younger stage that tends to become slightly inflated with growth. the more distinct, high radial ribs in right valve, and distinct radial ribs narrower than their interspaces and raised, rugose, fine incremental lines in the left valve. The present species also is related to A. antiguensis but it differs from the latter in having distinct, perpendicular sided radial ribs in right valve and the left valve with distinct, flatly rounded, broad radial ribs. It differs from A. preglyptus in having left valve with flatly rounded radial ribs that are nearly equal to their interspaces in younger stage, auricles with radial threads and distinct denticle at each extremity of hinge. Several poorly preserved specimens referable to the present species are known from an unnamed formation of Late Oligocene in Mexico. Type locality:— U.S. Geol. Surv., Loc. No. 19780. San Sebastián quadrangle, west of San Sebastián, Puerto Rico. San Sebastián Formation. Late Oligocene. Distribution:— San Sebastian Formation, Puerto Rico; Simojovel, Camino Carretero, Chiapas, Mexico (Univ. Calif. Berkeley, Loc. No. B8267); Late Oligocene.» KÔICHIRÔ MASUDA, 1971
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