Neithea whitneyi Kniker, 1919
KNIKER, H. T. 1919. Comanchean and Cretaceous Pectinidae of Texas. Bulletin of the University of Texas, 1817: 1-56, pls. 1-10 [p. 39, pl. 7, figs. 13-17]
1919 Neithea whitneyi Kniker, 1919
Neithea whitneyi n. sp.; H. T. Kniker, 1919, plate 7, figures 13-17.
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«Pecten wrighii Whitney, 1911, Univ. of Texas Bull. No. 184, p. 13, PI. I, fig. 4.
Dimensions. — Height 10 mm.; length 7 mm.; breadth 4.5 mm.
Description.— Shell small, subtrigonal, higher than long, almost equilateral; postero-dorsal margin slightly shorter than antero-dorsal margin. Anterior ear large and prominent, pointed, rounded transversely; posterior ear rudimentary, triangular and pointed. Ventral margin convex and sinuous. Right valve strongly convex, the beak considerably incurved, posterior slope' truncate. The ornamentation consists of four simple, but very prominent, subtriangular, radiating costae or ribs, with a smaller one at the posterior side. In addition to these, there is a minute rib near the anterior margin on the slope of the prominent anterior rib. The central costa is the most prominent one. The two adjacent ribs, which are practically equal, do not differ greatly from it. The anterior rib differs from the second one somewhat more than this latter differs from the central costa. The posterior rib is really a part of the posterior area. The central costa is separated from the two adjoining ones by moderately deep furrows slightly flattened at the bottom and practically equaling the ribs in width. The anterior and posterior ribs are separated from the1 others by narrower, angular depressions. At the ventral margin the ribs are produced as subtriangular extensions which have between them sinuses corresponding to the intercostal depressions. Over the whole surface are found fine concentric ridges barely visible to the naked eye. These are parallel to the undulated ventral margin and are inclined. From the anterior and posterior ribs the ridges are continued on the areas where they run parallel to the margin and are greatly crowded and become growth ridges. From the posterior area the ridges pass on to the posterior ear. On the anterior ear are seen concentric ridges and undulations. Humps which are probably due to growth thickenings are occasionally found on the ribs. The left valve is more or less flat. The eostae correspond to those of the right valve in ornamentation and relative size, but are more globose and somewhat more prominent, and the interspaces are comparatively wider than in the other valve. Growth ridges are found on both valves, especially along the ventral margin. The interior of each valve shows a distinct fluted border. Remarks. — The above is a description of a young shell. In older specimens the relative proportions are the same. On mature forms are found indications of the eostellae that are characteristic of N. wrighti. Affinities.—This species is distinguished from N. wrighti by its shape, which is more nearly equilateral, narrower, and more convex; by the ribs of its right valve, which are bluntly pointed at the summit, more solid, more triangular, and more prominent; and by its furrows, which are deep, narrow, and more or less angular, whereas those of the Georgetown form are broad and flat. Moreover, the ribs of the left valve of N. whitneyi are more prominent than those of N. wrighti, having steep sides, whereas those of the latter species have sloping sides. This form belongs to the same group as N. longicauda (d'Orb.) and N. cometa (d'Orb.). It is distinguished from the former by being more robust and shorter in proportion. In N. longicauda there are distinct costellae or secondary ribs on both valves, besides tubercles in the furrows of the left valve, which are all absent in the Texas species. Moreover, the ribs of the French form are broad, rounded, and low, whereas those of N. whitneyi are subtriangular, bluntly pointed, and high. In N. cometa there are broad rounded depressions between the narrow, sharp ribs, and prominent costellae contrasting withthe narrow furrows and prominent ribs of our species. In addition to this, N. whitneyi is shorter, broader, and has a less convex ventral margin than N. cometa. This form is relatively rare in the Buda Limestone. When Professor Whitney described it as P. wrighti a few years ago, the material on hand did not justify making it a new species. Number of specimens: 14. Occurrence: Lower division of the Buda Limestone, Austin and Manchaca, Texas.» HEDWIG THUSNELDA KNIKER, 1919
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