Neithella wrighti (Shumard, 1860)
SHUMARD, B. F. 1860. Observations upon the Cretaceous Strata of Texas. Transactions of The Academy of Science of St. Louis, 1: 582-610 [p. 607]
1860 Janira wrightii Shumard, 1860
Pecten (Neithea) wrighti (Shumard); T. W. Stanton, 1947, Studies of some Comanche pelecypods and gastropods, plate 21, figures 6, 7.
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«Shell ovate, subtrigonal, longest diameter from beak to base; superior valve flat or slightly concave, marked with three strong, rounded, plications, which are prolonged at the base into prominent angles; inferior valve strongly convex; anterior and posterior slopes abrupt, margins straight and diverging from the beak at an angle of about 40°; surface ornamented with four very prominent, simple radiating ribs or folds on the body of the shell, and one much less developed just within the margin on either side. Both valves are also elegantly marked with crowded, strongly waved concentric filiform striae; beaks elongated, slender, incurved; wings unknown.
Length, 6 lines; width, 8 lines. This shell differs from Janira occidentalis and J. Texanus in having a fewer number of ribs, there being no small ones in the intervals between the larger as in those species. Form. and Locality.— Two specimens of this shell were found by G. F. Wright, Esq., in the Washita Limestone (near base of Upper Cretaceous) on Shoal Creek, near Austin. It was rhere found associated with Janira Texana, and Terebratula Wacoensis.
The species is dedicated to Mr. G. F. Wright, to whose politeness I am indebted for the privilege of describing it.» BENJAMIN FRANKLIN SHUMARD, 1860
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«Description.— Shell large, subtrigonal, inequilateral, anterior, and posterior sides of approximately the same length. Anterior ear pointed, prominent, surface rounded transversely; posterior ear rudimentary. Ventral margin sinuous.
Right valve convex, beak incurved, posterior slope truncate. On this valve are found four prominent rounded ribs, which have a prominent costella at the summit. This gives them an angular appearance. A smaller costa is found at the posterior side of the shell, while a still smaller inconspicuous one is found on the slope of the anterior rib near the anterior margin, The middle costa is the most conspicuous one, but is practically equal to the adjacent one on the posterior side. The two anterior ribs are almost equal, but the most anterior one curves outward considerably and is higher. The costae are separated by broad, unequal, flattened depressions. The depression anterior to the middle costa is the widest one, being somtewhat wider than this costa. Posteriorly to the middle and to the most anterior costa are found furrows practically equal to these ribs. At the base of the shell the ribs are prolonged into prominent extensions which are separated by broad, rounded sinuses corresponding to the intercostal depressions. Left valve almost flat. The costae. correspond to those of the right valve and have similar ornamentation. As in Neithea whitneyi. sp., growth ridges are found on both valves, especially near the base and on the anterior ear. Each valve has a fluted border on the interior side. Remarks.— Cragin (5, p. 217) inhis discussion of this species, says: ''Summits of costae inboth valves formed, in each instance, by a somewhat salient round-backed costella, there being on the two slopes and included valley which constitute the surface between any two summit-costellae, ten or twelve feebly elevated radial costellae delimited by impressed strife and crossed by innumerable raised lines of such fineness as to be barely visible to the naked eye." The costellae are not always so pronounced on our specimens, nor arranged in so regular a fashion as described by Cragin and shown in his drawings or N. wrighti. The "raised lines" are distributed on this species as on N. whitneyi n. sp.
In the original description of this species, costellae are not mentioned. This is probably explained by the fact that this ornamentation is often very indistinct on young individuals, and, according to Shumard's measurements, his was an immature specimen. «Affinities.— The species described under the name of N. whitneyi, n. sp. differs from N. wrighti in several ways, which are mentioned in that description. N. wrighti is distinguished from N. cometa (d'Orb.) and N. longicauda (d'Orb.) by its shape, which is more inequilateral and broader; and by its ears, which are smaller and more triangular. Furthermore, the interspaces are flat or flattened in N. wrighti, whereas they are rounded in the French forms. In N. longicauda the ribs of the right valve show distinct costellae, are very broad, and the intercostal spaces are narrow, and there are prominent costellae and tubercles on the left valve. Thus, this species differs considerably from ours in ornamentation.»
KNIKER, H. T. 1919. Comanchean and Cretaceous Pectinidae of Texas. Bulletin of the University of Texas, 1817: 1-56, pls. 1-10. [p. 24, 25]
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Neithea wrighti (Shumard); H. T. Kniker, 1919, Comanchean and Cretaceous Pectinidae of Texas, plate 4, figures 1-3.
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