Leptopecten nelsoni (Olsson, 1932)
OLSSON, A. A. 1932. Contributions to the tertiary Paleontology of Northern Peru: part 5. The Peruvian Miocene. Bulletins of American Paleontology, 19 (68): 1-272, pls. 1-24 [p. 82, pl. 5, figs 3, 6]
1932 Pecten (Plagioctenium) nelsoni Olsson, 1932
A. A., Olsson, 1932, plate 5.
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«Shell of medium size, thin, nearly equivalve and only slightly convex; right valve with about 16, low, rounded to triangular-shaped ribs separated by flattened interspaces; the ribs and interspaces are clearly separated and distinct on the nepionic portion of the valves but on the ventral portion, the ribs become lower, flatter, their sides merging gradually into the interspaces; on the left valve the ribs are similar but narrower and with wides interspaces. The nepionic half of the valve is smooth while the lower half is covered with fine, even, crowded, raised concentric threads; ears typical and probably subequal in size, only the right posterior and the left anterior preserved in our specimens; the right posterior is flattened with two, thread-like radials and fine growth-lines; the left, anterior ear similar but with a wide, shallow notch opposite the deep byssal notch of the right valve and ornamented with five, irregularly spaced, radial threads and fine, concentric threadlets; interior of shell fluted in harmony with the external ribs.
Height, 41 mm.; breadth, 44 mm.; semidiameter, 5 mm. (right valve). Remarks.—This species resembles Pecten coderensis Harris [Harris, 1927, In Hodson, Bull. Amer. Pal., vol. 13, p. 34, pl. 18, figs. 2, 4, 5] from Venezuela. In coderensis, the ribs are flatter and the surface of the shell is nearly smooth, the concentric growth-lines being very faint. In nelsoni however, the nepionic or upper part of the valves have a smooth sculpture changing sharply to one of coarse raised, concentric threads on the lower half. Locality and Geologic Occurrence.—Tumbez formation, Que. Tucillal.» AXEL ADOLPH OLSSON, 1932
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