Neithea casteeli 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. 51, pl. 10, figs. 7-11]
1919 Neithea casteeli Kniker, 1919
H. T. Kniker, 1919, plate 10.
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«Dimensions. — Height 28 mm.; length 26 mim.; breadth 10 mm. (distorted specimen.)
Description. — Shell large, subovate, almost equilateral; height slightly greater than length; base board, angular; antero-dorsal and postero-dorsal margins long; greatest length below the middle. Ears large; hinge line straight. Right valve gently convex, umbo broad and incurved. This valve is decorated with twenty-six prominent radiating ribs. Every fifth one, including the most anterior and the most posterior, is distinctly elevated. The ribs curve moderately outward. Among the ribs in the depressions the two middle ones, which are practically equal, are sometimes stronger than the other two. More often three are of practically the same size, and an external one is smaller. The two outer ones usually differ somewhat in size. The prominent ribs are appreciably higher than those in the depressions, and almost twice- as wide as the widest in these groups. The ribs are rounded, and the depressions are flat. The most posterior (prominent) rib is split by a radial sinus. The intercostal spaces are rounded, subequal, and usually narrower than the ribs. An exception to the latter characteristic is often found in the first and the last group, where the strength of the ribs is reduced. As in similar species, the extensions of the prominent ribs form, the angles at the base. The concavities between these projections are not very deep. The antero-dorsal area is not preserved, but on the posterodorsal there are very prominent secondary ribs. Six can be made out distinctly and a few more may have been obliterated by weathering. They are relatively broad, high, and rounded, and decrease in size as they are located nearer the margin. However, they are continued on the ear, where they are very prominent and numerous. Fine, regular, concentric lines cover the ribs, interspaces, areas, and ears. The left valve is flat or somewhat concave. The ornamentation consists of subequal, radial ribs, corresponding to the interspaces of the right valve. The ribs are subtrigonal in shape, rounded on top, and narrower than the intercostal spaces. The two ribs adjoining the furrows corresponding to the raised ribs of the right valve, are elevated above a group of three on each side, that lie in a slightly concave depression. Hardly any two adjoining ribs are of the same strength. Most of the broader ones are elevated, thus showing that the corresponding furrows at the side of prominent ribs of the right valve are wide. On this valve are found concentric ridges arranged as on the right valve. Only fragments of this valve have been collected. Remarks. — Attention has been called to the fact that the ribs in the depressions of the right valve vary in strength. In one of the depressions of one specimen there are onlythree ribs. This leads the writer to believe that probably the same variations exist in the Texas form that have been observed in N. quinquecostata by European paleontologists. It is very seldom that one of the small exterior ribs in the depressions is so near the prominent rib as to seem to be connected with it. Usually a broad furrow separates the two. This is indicated also by the raised ribs of the left valve, which are often exceptionally broad. Affinities.— Roemer (19, p. 64), Conrad (3, p. 269), Gabb (10, p. 366) and Boese (1, p. 99) have pointed out that the quinquecostata form of North America is distinct from the typical N. quinquecostata. Roemer (19, p. 64) desribed a quinquecostata form from Fredericksburg as Pecten quadricostata var. His right valve differs from ours inhaving a fine linear rib on each side of the prominent rib, combined more or less with this latter, thus giving the raised ribs a trifid appearance. With regard to the left valve, he says: "Je vier Rippen sind buendelweis gweissermassen zu einer einzigen flachen Rippe vereinigt und die Mitte des Zwichenraums zwischen je zwei solchen breiten, flachen Falten nimmt eine einzelne schmale gerundete Falte ein. Die breiten aus der Vereinigung von vier entstehenden Falten entsprechen uebrigens in ihrer Lage den fuenf staerkeren Rippen der anderen Klappe und stossen mit diesen am Rande zusammen." There is no such arrangement on the left valves of N. casteeli n. sp. Moreover, Roemer 's shell is higher and has shorter areas than N. casteeli, and the author does not mention secondary ribs on the areas and ears. Conrad (3, p. 269; 4, p. 150, pl. 5, fig. 1) lists Roemer 's quadricostatus var. as synonymous with his occidentalis. His species differs from the writer's inbeing higher, in having shorter areas, and in not having fine ribs on the areas and ears. Neithea quinquecostatus (Mort.) (15, p. 57, pl. 19, fig. 1) was included by Gabb (10 p. 365) in his species Neithea mortoni. Gabb, in speaking of the left valve, says: "There is, very rarely, the slightest approach to the sexradiate arrangement of the other valve." As has been mentioned in the description above, this arrangement is very pronounced in N. casteeli. Furthermore, there seems to be a greater variation in the strength of the ribs of the Texas species. Judging from Morton's figure, there are certain definite differences between the shape of N. quinquecostatus Mort. and N. casteeli. Since Gabb considers Roemer's quadricostata var. identical with his species, and, since the writer believes the former to be distinct from N. casteeli, N. mortoni is regarded as distinct from N. casteeli. Boese's N. quinquescostata is not closely related to the other American quinquecostata forms, since the latter are Upper Cretaceous species. His specimens came out of Lower Cretaceous Formations. Number of specimens: About 40. Occurrence: Austin Chalk, Austin, Texas» HEDWIG THUSNELDA KNIKER, 1919
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«On the Gulf coastal plain, Pecten aff. P. quinquecostata illustrated by Stephenson (1926, pl. 92, fig. 11) and Pecten quinquecostata of Wade (1926, pl. 21, figs. 1-5) from the Ripley Formation of Alabama and Tennessee, respectively, are probably not this species. However, Neithea casteeli Kniker (1918, pl. 10, figs. 7-11) from the Austin Group appears to be synonymous with N. (N.) quinquecostata.»
ELDER, W. P. 1996. Bivalves and gastropods from the Middle Campanian Anacacho Limestone, south central Texas. Journal of Paleontology, 70 (2): 247-271, figs. 1-8. [p. 254]
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