Chlamys (Lyropecten) madisonius bassleri Tucker-Rowland, 1938
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. 13, pl. 5, fig. 1]
«Chlamys (Lyropecten) madisonius bassleri, subsp. nov.
Pl. V, fig. 1. DESCRIPTION. — Shell very thin, somewhat ovate; the left valve convex, right nearly flat, or only slightly convex. Sixteen narrow ribs, each carrying a row of erect spines; about 20 mm. from the beak a secondary row of spines appears on either side of each rib. Ribs wider at the base. lnterspaces rounded, with closely spaced, erect rows of spines which extend up the sides of the ribs. One or two of the rows of spines frequently more promirrent.
Submargins have radial sculpture of prickly radials. Aulicles unequal; radially threaded with fine rows of small, erect spines. Ribbed internally to the umbones. Individuals fairly close to this subspecies occur at Church View, Va. Left valve quite convex, right nearly flat; 15 ribs. A left valte, in the collections of Cornell University, from Plum Point, Md., has a somewhat shorter byssal auricle than madisonius, s.s., is more ovate; ctenolium present; fasciole wide. This subspecies is named in honor of Dr. R. S. Bassler, of the U. S. National Museum. REMARKS. — C. madisonius bassleri is smaller, and the shell is thinner than that of madisonius, s.s. The development of scaly sculpture is more pronounced; ribs more numerous and narrower; left valves more convex; more nearly oval in outline. This subspecies tends to be larger than coccymelus, has fewer ribs; a single row of scales on the summits of the ribs; less conspicuous scaly sculpture; longer hinge line; more strongly convex. This subspecies appears to be quite characteristic of the Maryland Calvert. DIMENSIONS. — Holotype, height 58, width 46, convexity 16, hinge 31.5 mm. LOCALITIES. — Plum Point (type), and Chesapeake Beach, Md. HORIZON. — Calvert (Miocene). HYPOTYPES. — Collection Cornell University; collection H. I. Tucker-Rowland. HOLOTYPE. — U. S. National Museum. Cat. Nº 145919.» HELEN IONE TUCKER-ROWLAND, 1938
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H. I. Tucker-Rowland, 1938,
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