Neithea austinensis 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. 46, pl. 9, figs. 4-6; pl. 10, fig. 2]
1919 Neithea austinensis Kniker, 1919
H. T. Kniker, 1919, plates 9, 10.
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«Dimensions. — Height 32.5 mm.; length 28.5 (?) mm.;breadth 10.5 (?) mm.
Description.— Shell rather large, subtrigonal, practically equilateral, solid; ventral margin shows six blunt projections formed by the prolongations of the six prominent ribs. Ears triangular and medium; hinge line straight. Eight valve moderately globose, umbo gently incurved. This valve is decorated with sixteen prominent and rather high radiating ribs of which every third one, including the most anterior and the most posterior, is somewhat stronger and is raised slightly above the others. There is an unusual arrangement of the two ribs in each depression. These ribs are close together and are separated by a furrow that is shallower than those by the side of the prominent ribs. The ribs appear to be rounded, but upon closer investigation it is found that they are flattened to some extent. The intercostal spaces adjoining the raised ribs are flattened and are as wide as, or slightly wider than, these latter. The ribs inthe median depression are separated by a very narrow groove scarcely half as wide as one of these ribs. In the depressions anterior and posterior to the median one, the corresponding groove is slightly wider. And in the two remaining depressions grooves and ribs are practically equal in width. However, the ribs in the latter depressions are greatly reduced in size. As in similar species, the anterior ear is separated from the shell by a deep groove, while the posterior ear curves outward from the posterior area. This valve is further ornamented with delicate radial ridges. From two to five or more can be made out on each rib. In the intercostal spaces they are not so abundant, and not more than two have been noticed in any one space. Better material might show these ridges distributed ina regular manner. On the areas there are very fine radiating ribs. The number is not constant, but usually there are five, and they are distributed over the whole surface of the area. Fine, crowded, concentric lines cover the whole shell and the ears. The left valve is flat and is ornamented with fifteen principal radiating ribs, the ribs corresponding to the depressions on the right valve. The ribs that correspond to the furrows by the side of the prominent ribs of that valve, are the raised ribs of the left valve. They are broad and flattened and appear in pairs. In the depression between two adjoining pairs, there is a low, narrow, sharp rib. As on the right valve, there are found radial ridges or fine secondary ribs on these ribs, distributed inan irregular manner, and more on the ribs than in the interspaces. A few fine secondary ribs are present on each area. On the posterior ear there are some marks which indicate that perhaps several small, radiating ribs are present near the hinge line. However, the specimens are not well enough preserved to determine them definitely. Delicate, yet distinct, concentric lines cover the whole shell. They are somewhat stronger on the ears. Affinities.— N. austinensis n. sp. differs from all similar Texas Comanchean and Cretaceous Neitheas in having the two ribs in the depressions close together and separated by a furrow that is shallower than the other interspaces. This species differs from N. budensis n. sp. in being less globose, in having radial ridges on the ribs and in the depressions, in not having its prominent ribs trifidin character, and in the general shape of the ribs. Moreover, the left valves are entirely different. From N. georgetownensis n. sp., N. austinensis n. sp, differs in its form, which is much less convex and not so solid;inthe ribs in the depressions of the right valve, which are higher and more rounded, inthe raised ribs of this valve, which are not so prominent; in the ornamentation of radial ridges on both valves, which, however, have a parallel in the stronger riblets and depressions on the shell of N. georgetownensis. Number of specimens: About 25. Occurrence: Austin Chalk, Austin, Texas.» HEDWIG THUSNELDA KNIKER, 1919
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