Chlamys riggsi Zinsmeister, 1981
ZINSMEISTER, W. J. 1981. Middle to Late Eocene Invertebrate fauna from San Julián Formation at Punta Casamayor, Santa Cruz Province, Southern Argentine. Journal of Paleontology, 55: 1083-1102, pls. 1, 2. [p. 1094, pl. 2, figs. 1, 2]
«CHLAMYS RIGGSI n.sp.
Pl. 2, figs. 1, 2 Description.— Medium size, equilateral, moderately convex right valve, disk flanks moderately steep; 6 primary folds, posterior and anterior folds greatly reduced; second and third fold on anterior half of dish strongly bifurcated into two folds; crests of folds ornamented
with strongly developed costae, 5 to 6 present only non-bifurcated folds; 3 to 4 on bifurcated folds; interspaces ornamented with narrow costae which tend to become narrower in center of interspaces; costae in interspaces tend to become obsolete near umbones; crests of costae squamose; squamae delicate on costae in interspaces; auricles with 5 to 6 squamose radiating ribs; 5 to 6 denticles byssal notch. Dimensions.— Holotype P28891a, height 77 mm, width 81 mm; paratype P288916, height 91 mm, width 88 mm (incomplete). Repository.— Field Museum of Natural History, Chicago, Illinois. Discussion.— C. riggsi n.sp. shares a number of common characters with C. proximus Ortmann, but may be separated by the development of marked bifurcation of second and third anterior folds. Interspace costae tend to extend from margin to umbo, while on C. proximus the interspaces are smooth on young individuals. The size of C. riggsi is only about a third of C. proximus from the Rio Santa Cruz. The similarity of C. riggsi and C. proximus indicates that the two species are closely related and form a distinct lineage during the Late Eocene through the Oligocene. This species is named in honor of Elmer S. Riggs for contributions to our understanding of Tertiary faunas from southern South America.» WILLIAM J. ZINSMEISTER, 1981
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W. J. Zinsmeister, 1981, plate 1.
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