Neithea budensis 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. 36, pl. 7, figs. 4-12]
1919 Neithea budensis Kniker, 1919
H. T. Kniker, 1919, plate 7.
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«Dimensions. — Height 22 mm.; length 18 mm.; breadth 10 mm.
Description.— Shell medium to large, subtrigonal, slightly higher than long, equilateral. Ears conspicuous, but not well preserved on the type. Other specimens show the anterior ear to be short and triangular and separated from the body of the shell by a groove. The posterior ear appears to be larger and is a continuation of the posterior area. Basal margin sinuous. Right valve ventricose, umbo curved over the hinge line which is short. Decorations consist of six prominent trifid ribs radiating from the umbo to the angles of the ventral margin, with two smaller ribs in the depressions between these raised areas. Two of these areas form the anterior and posterior boundary of the ribs. The three ribs on the prominent ridges are arranged in a characteristic manner. The middle, rib is the highest one and is smaller than the two ribs in the depressions, but approaches them in width. The fourth ridge is the center of symmetry. Here is found the only exception to the trifid arrangement. Instead of a more prominent rib between the other two, there are, in this case, two smaller ribs in place of the central one. They are equal, are on top of the ridge, and separated by a gently rounded depression equaling them in width. Halfway down on the posterior slope is a smaller rib separated from the adjoining ribs on top of the ridge by a very narrow depression. On the lower part of the anterior slope there is a conspicuous rib somewhat stronger than the two on top of the ridge. The arrangement of the ribs on the fifth and sixth ridges is the reverse of that on the first three. In each case the middle rib is the larger one. On the extreme upper portion of the slope on all five ridges there is a slightly smaller rib on the side towards the center of symmetry. On the other side, at the base of the slope there is a rib similar to the other secondary ribon the same ridge. All ribs are flattened on top and have almost perpendicular sides, which give them a rectangular appearance. The two ribs in the depressions are, relatively speaking, higher than those on the ridges, so that they extend upward almost as high. The ribs on the ridges are, for the most part, separated by very narrow furrows. This is, however, not the case in the depressions, which are flat as a whole. The different ribs have between them gently curved narrower depressions. At the base the ridges form irregularly curved projections which are separated by sinuses that are practically equal to them. This species is further ornamented with very pronounced growth ridges, which are so prominent that they give the ribs a ropy appearance. Ribs are absent on the areas, but prominent lines of growth are found here. The ears are covered with similar crowded, concentric lines. Not all of the specimens show the above ornamentations completely. The shells weather easily. This obliterates the concentric striae and often the ribs on the ridges. In this condition these prominent areas have the appearance of smooth elevations that have had a few radial lines impressed upon them. The ribs in the depressions are protected and are not affected so much. No perfect left valves have been collected. This valve is slightly concave and has six elevated areas corresponding to those of the right valve. As far as can be determined, the arrangement of ribs on the areas seems to be more regular than on the right valve. Here are found three ribs, practically equal, on top of the ridges. On the fourth ridge there is added a smaller rib on the posterior slope. There are two larger ribs in each depression. The furrows separating the ribs are practically equal to the latter in width. The shape of the ribs, and pronounced concentric lines correspond to those of the right valve. Affinities.—This species is perhaps a descendent of N. irregularis. In that form secondary ribs are distributed in an irregular manner. Here the six raised ribs have practically disappeared, and ridges have taken their place wath secondary ribs grouped upon them in a definite manner. Besides this difference, there are other definite ones. The shape of the ribs is entirely different in the two forms. Also, N. budensis is more globose and not so high. In the left valve there are ridges covered with ribs in N. budensis in contrast to the double ribs in N. irregularis. Shattuck and Boese have described a form from the Lower Cretaceous as N. quinquecostata. Evidently N. budensis, or a similar species, was the basis of the description of these two authors. Number of specimens: 21. Occurrence: Both divisions of the Buda Limestone, Austin Round Rock, and Manchaca, Texas.» HEDWIG THUSNELDA KNIKER, 1919
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