Pecten costaricensis Olsson, 1922
OLSSON, A. A. 1922. The Miocene of Nothern Costa Rica with notes on its general stratigraphic relations. Bulletins of American Paleontology, 9 (39): 1-460, pls. 1-32. [p. 373 (201), pl. 18, figs. 8-11]
«Pecten costaricensis, n. sp. Plate 18, figures 8-11
Shell small, inequivalve, oblique; the right valve is moderately convex, the left but slightly; right valve with 17 flat-topped ribs, square in section and with deep U-shaped interspaces of a width equal to the ribs; these interspaces are sculptured with fine, concentric, raised lines which are quite far apart on the umbos, but become crowded ventrally or disappear entirely; the left valve has 17 or 18 ribs which are lower and more rounded in section; the fine concentric lines on the left valve are confined to the umbos, the interspaces over the greater part of the shell being smooth; the anterior and posterior dorsal slopes are flattened and smooth, but sculptured below in each valve by strong radial threads on the lower side of the ears; ears subequal; the right valve with a deep, byssal notch in its anterior ear; the left valve has the lower half of each ear with 3 strong radial threads, while on the upper half, the radial threads are largely obsolete; valves internally grooved in harmony with the external ribbing to about the center of the shell.
Differs from the Pecten levicostatus Toula, by its unequal valves, less convexity and fewer ribs. It is somewhat like the Pecten inaequalis Sowerby, from which it is distinguished by its more flatte ed left valve and lower, smaller ribs of its right. In inaequalis, the fine, lamellose, concentric lines cover the entire interspaces between the ribs on both valves, while in the present species the interspaces of the left valve are largely smooth with the concentric lines confined to the extreme umbonal area.
AXEL ADOLPH OLSSON, 1922
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A. A. Olsson, 1922, plate 18.
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