Chlamys (Lyropecten) madisonius richardsi Tucker-Rowland
TUCKER-ROWLAND, H. I. 1938. The Atlantic and Gulf Coast Tertiary Pectinidae of The United States. Section III Systematic Descriptions. Mémoires du Musée Royal D'Historie Naturelle de Belgique [2me Série], 13: 1-76, pls. 1-6. [p. 14, pl. 3, figs. 4, 5]
«Chlamys (Lyropecten) madisonius richardsi, subsp. nov.
Pl. III, fig. 4, 5. Pecten madisonius Say, variety, MANSFIELD, U. S. Nat. Mus., Proc., 74: pl.2, fig. 1, pl. 3, fig. 1, 1929.
DESCRIPTION. — Left valve quite convex: 15 somewhat elevated slightly rounded ribs, usually with 3 faint radial threads on the summits. In the umbonal area the ribs tend to be narrow, more or less flat-topped. One strong radial thread in each interspace, which extends to the umbones; usually 2 weaker radial threads. Surface of disk, and submargins strongly sculptured with wavy, elevated, concentric lamellae which tend to be more closely spaced at the ventral margin. Submargins indistinctly treaded radially. Auricles unequal; concentric lamellae tend to form tiny linguiform processes on the summits of the radial threads. Right valve has 14 ribs; sculpture similar to that of the left valve. Byssal auricle the more coarsely sculptured; 6 strong radials. Fasciole wide, conspicuous, not deep. REMARKS. — This subspecies is apparently rather closely related to urbannaënsis Mansfield, which also occurs in Zone 2 of the St. Marys. Perhaps eboreus, s.s., was derived from such forms as urbannaënsis and richardsi. Typical eboreus appears in the Suffolk beds (Upper Yorktown) for the first time. This subspecies has a less elongated byssal auricle than madisonius, s.s.; the interspaces are somewhat more shallow; the characteristic scaly sculpture of madisonius is not developed. It has the general appearance of eboreus, with the radial sculpture of madisonius. DIMENSIONS. — Syntypes: Left, height 80, width 80, convexity 18 mm.; right, height 89.5, width 89.5, convexity 10 mm. LOCALITY. — Grays Creek, Surry County, Va. (type). HORIZON. — Zone 2, St. Marys (Miocene). SYNTYPES. — Right and left valves of different individuals, U. S. National Museum, Cat. Nº 370830» HELEN IONE TUCKER-ROWLAND, 1938
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H. I. Tucker-Rowland, 1938,
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