Neithea simondsi 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. 41, pl. 8, figs. 1-10]
1919 Neithea simondsi Kniker, 1919
H. T. Kniker, 1919, plate 5.
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«Dimensions. — Height 5.5 mm.; length. 5mm.; breadth 2 mm.
Description. — Shell small, almost as long as high; ventral margin semicircular and rounded. Ears subtriangular and relatively large; hinge line straight and short. Right valve moderately convex, umbonal slope gently curved over the hinge line, antero-dorsal and postero-dorsal margins relatively long. This valve is ornamented with nineteen prominent, flattened, radiating ribs of which every fourth one, beginning at the anterior and posterior borders, is slightly raised, in the umbonal region, above the three at each side, which lie in a broad, shallow, gently sloping valley. In the middle and the basal regions of the shell, however, all ribs are of the same height. The four ribs that are raised on the umbo are always somewhat wider than the others. The ribs are separated byrather deep, narrower, flattened depressions. Adjoining the four wide ribs are found furrows wider than those that separate the other ribs. Moreover, all ribs are scaly on the umbo and for some distance farther down on the valve. The anterior ear is separated from the body of the shell by a groove, while the posterior one is an extension of the posterior area. Both areas and ears are covered with prominent concentric ridges, and the former show no secondary ribs. However, on a few specimens a shallow depression has been noticed on the areas and adjoining the ribs, but itdies out before reaching the umbonal regions. The left valve is missing. Remarks. — On weather specimens the scales on the ribs are indistinct or entirely obliterated. One of the specimens shows a modification of the ordinary arrangement of ribs. Instead of having four wider ribs, it shows four groups of two wide ribs each. There are three narrower ribs in the median group of the valve, but at the other places there are only two. Thus, the usual number of nineteen is retained. Affinites.— Of all the Texas Cretaceous Neitheas heretofore described, N. bellula (Crag.) resembles N. simondsi n. sp. most. There is a general similarity between the shape of the shell and the shape of the ribs of the right valve of the two species. But the facets and varying number of ribs in each, so characteristic of the former species, are not found on the latter. In N. simondsi there is regularity inthe distribution of ribs. There are always three ribs between two wider ones, and the wide ribs are never replaced by twin-ribs or a group of very narrow ribs. Here are found only four wide ribs, whereas there are six such areas in N.bellula. Furthermore, the number of ribs in N. bellula is more than twice that in N. simondsi. This species is distinguished from N. irregularis (Boese), N. subalpina (Boese), N. texana (Roem.), and allied species principally in having three ribs between two broader ones and having all of the same height, except in the umbonal regions, whereas in the forms mentioned above there are only two principal ribs between the prominent ones, and every third rib is distinctly raised. Moreover, there are no secondary ribs on the areas of N. simondsi n. sp., which is not the case in these other species. N. simondsi n. sp. differs from N. boesi n. sp. incertain respects that are mentioned in the discusson of that species. The former species can be easily distinguished from N. laevis Drouet by being higher and having totally different ribs. Number of specimens: 13. Occurrence: Both divisions of the Buda Limestone, Austin, Manchaca, and Round Rock, Texas.» HEDWIG THUSNELDA KNIKER, 1919
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