Leopecten Masuda, 1971
MASUDA, K. 1971. Patinopecten from North America. Transactions and Proceedings of the Palaeontological Society of Japan [N. S.], 83: 166-178, pls. 19-21. [p. 170]
«Subfamily Amusiinae
Genus Leopecten MASUDA, n. gen.
Type-species:— Pecten (Patinopecten) bakeri HANNA and HERTLEIN, 1927. Pliocene. Baja California, Mexico.
Geological and geographical distribution:— Early Pliocene to Late Pliocene. Baja California, Mexico.
Diagnosis:— Shell large, gently inflated, of medium thickness, longer than high, equilateral, subequivalve, right valve a little more inflated than left valve which is nearly fiat in younger stage but tends to become inflated with growth; right valve with distinct, per· pendicular sided, flatly round·topped radial ribs which are sculptured with sometimes faint, fine radial threads, fine intercalary threads and fine, rugose incremental lines; left valve with distinct but low, narrow radial ribs usually sculptured with a few faint, fine radial threads, a few fine intercalary threads, and raised, regularly spaced, rugose, fine incremental lines; auricles large; right anterior auricle angulated at end, with very wide and shallow byssal notch; hinge with very simple, low, fine cardinal crura with fine provinculum and wide and shallow resilial pit; auricular crura well developed, terminating distally in a distinct oblong denticle at each
extremity; interior surface with distinct paired internal ribs at lower part. Remarks:— The present new genus is named in honor of Dr. Leo G. HERTLEIN of the California Academy of Sciences.
The present genus resembles Patinopecten externally but Patinopecten lacks paired internal ribs and has a well developed byssal notch below the right anterior auricle. Amussiopecten (SACCO, 1897, p. 55) is closely related to the present genus but it is distinguishable from Leopecten by its radial ribs which tend to become obsolete towards the ventral and lateral margins, lack of radial threads on the surface of the radial ribs and no intercalary threads in the interspaces between the radial ribs. The morphological characteristics of these two genera are somewhat similar to each other in their younger stages but the surface sculpture in the adult stage is quite different. That is to say, it seems that the general morphologic characters in the younger stage of Amussiopecten are retained in the adult stage in Leopecten. Therefore, it is inferred that Leopecten may have descended from Amussiopecten before the Early Pliocene, but no intermediate form is known between the two. Flabellipecten (SACCO, 1897, p. 55) is distinguishable from the present one by its rather more inflated right valve, plano-convex left valve, rather small auricles and more distinct and complicated cardinal crura. Considered from the standpoint of the associated fauna, it appears that Leopecten might have been a tropical or subtropical inhabitant as was Amussiopecten. This new genus includes the following species: Pecten (Patinopecten) bakeri HANNA and HERTLEIN, 1927, Patinopecten bakeri diazi DURHAM, 1950 and Patinapecten marquerensis DURHAM, 1950.» KÔICHIRÔ MASUDA, 1971
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Leopecten bakeri (Hanna and Hertlein); K. Masuda, 1971, Patinopecten from North America, plate 20,
figures 1, 2. |
Pecten bakeri Hanna & Hertlein, new species; G. D. Hanna & L. G. Hertlein, 1927, Expedition of the California Academy of Sciences to the Gulf of California in 1921, Geology and Paleontology, plate 5, figure 1.
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«Family PECTINIDAE Rafinesque, 1815
Subfamily PECTININAE Rafinesque, 1815 Genus LEOPECTEN Masuda, 1971a Type species.— Pecten (Patinopecten) bakeri Hanna and Hertlein, 1927, by original designation, San Marcos Formation, Pliocene, Baja California Sur, Mexico.
Diagnosis.— Pectininae with right valve of low to moderate convexity; left valve much less convex and of changing curvature through ontogeny, flattened or concave early state followed by flat to convex final stage resulting in overall curvature from slightly concave to convex; hinge dentition simple, consisting of weak dorsal teeth and even weaker resilial teeth, intermediate teeth vestigial or absent, apposition zone of hinge (‘‘provinculum’’ of Masuda, 1971a) with very fine striae perpendicular to hinge line. Disk with weak to moderately strong simple plicae ranging in cross section from triangular with carinate crest to rectangular with flattened crest. Commarginal lamellae present across disk in early ontogeny, commonly restricted to interspaces in late ontogeny. Radial costellae sometimes present on plicae and in interspaces. Right anterior auricle with few radial costae early in ontogeny, then noncostate. Right posterior auricle commonly without costae. Left auricles generally with only one or two very weak costae in dorsal half, less commonly three widely spaced costae, or with multiple costae beginning late in ontogeny after initial stage with only one or two costae. Fine columnar prismatic calcite present in early ontogeny of right valve terminating at valve height from 5.5 to 10 mm. Inner surfaces of plicae with carinate margins distally. Inner ostracum foliated, including all of nonmyostracal area inside pallial line.
Occurrence.— Stratigraphic range from Lower Miocene to present; geographic range western South Atlantic and Caribbean in Miocene, extending into eastern Pacific in Pliocene, and restricted to eastern Pacific in Pleistocene and Holocene.»
WALLER, T. R. 2007. The evolutionary and geographic origins on the endemic Pectinidae (Mollusca: Bivalvia) of the Galápagos Islands. Journal of Paleontology, 81 (5): 929-950, figs. 1-9. [p. 945]
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