Neithea georgetownensis subirregularis 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. 33, pl. 6, figs. 4-5]
1919 Neithea georgetownensis var. subirregularis Kniker, 1919
H. T. Kniker, 1919, plate 6.
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«Description.— There are in the writer's collection some specimens which resemble Neithea georgetownensis in shape and proportions, but have smooth ribs. It is a fact that there is considerable individual variation inJV\ georgetownensis (see Remarks on that species), but the ribs are always split. On the specimens under consideration, there are found occasionally a few fine intercostal ribs distributed in an irregular manner on the valve, but the main ribs are always without furrows and costellae. Consequently, there are very globose, rounded, and prominent raised ribs, and ineach depression two narrower subequal and very low, flat ribs. The relation between width of ribs and intercostal spaces varies in different specimens. In fact, there is a series of gradations. Ordinarily, the ribs are appreciably wider than the spaces, but the width of the former gradually decreases until it approximates that of the spaces.
The left valve is missing. Affinities.— This form is similar to N. texana var. elongata, because of its rounded raised ribs, and flat ribs in the depressions. However, there are great differences between the two. N. georgetownensis var. subirregularis is more blobose than the above mentioned variety, and there is a greater difference between raised and low ribs. In N. texana var. elongata the prominent ribs are raised only slightly above the others, and all are of practically the same width, while in N.georgetownensis var. subirregularis the raised ribs arc far more conspicuous and wider than the others, and these latter are very low and flat, lower than those of the former species. Number of specimens: 30. Occurrence: Georgetown Limestone, Austin, Texas.» HEDWIG THUSNELDA KNIKER, 1919
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