Euvola caribea (Weisbord, 1964)
WEISBORD, N. E. 1964. Late Cenozoic Pelecypods from Northern Venezuela. Bulletins of American Paleontology, 45 (204): 1-564, pls. 1-59. [p. 121, pl. 12, figs. 1-2; pl. 23, figs. 6-8]
N. E. Weisbord, 1964,
plates 12, 23. |
«The following description pertains to the right (lower, convex) valve.
Shell large, fairly thin, nearly equilateral, inflated, somewhat wider than high, the disk fan-shaped. Hinge line straight, dorsal margins concave and diverging from the beak at an angle of about 108 degrees, ventral margin semicircular. Dorsal slopes short and steep, the margin of the disk subrounded below the ears, excavated opposite the ears which are slightly sunken. Auricles a little unequal, the anterior one subtruncate at the margin and notched at the base, the posterior ear sharply squared off at the nearly vertical margin. Both ears are radiately ribbed below, obsoletely ribbed above, the anterior ear with about five subequal ribs in all, of which the lowest one adjacent to the fasciolar groove is the strongest, the others, particularly the uppermost one or two, progressively weaker; posterior ear with about four radial ribs, the upper one nearly obsolescent, the upper third of the ear smoothish. Crossing the ears are numerous sinuous concentric growth striae. The inner surface of the anterior ear is shallowly fluted in consonance with the external ribbing, and the edge is gently scalloped. Beak small, triangular, appressed, the point even with the hinge line. Chondrophore small, triangular, deep, the sides a little thickened, and merging, in a sort of dog-leg, with the low rounded cardinal crura running along the inner margin of the ears, the anterior crura more pronounced than the posterior. There is no cardinal ridge under the ligamental groove of the anterior ear but there is a faint arcuate one on the posterior ear, the ridge curving down obliquely from the distal end of the ear to join the upper part of the cardinal crura. Ctenolium with four small teeth, these disappearing or covered in adults. Exterior sculptured by a total of 23 radial ribs of which the two at either margin of the disk are paired, the outer rib of each pair the smallest of the disk, the submargins of the valve smooth. The ribs are squarish but gently rounded at the summit, generally regular, although occasionally feebly grooved medially, and separated by squarish interspaces about half the width of the ribs. Crossing the interspaces, but smoothed off on the crest of the ribs, are regularly spaced fine concentric lamellae which become crowded at the base of the disk. Internal ribs about 20, the interspaces narrow and shallow except at the ventral margin where they become deeper flutings nearly as wide as the ribs themselves; near the base, the ribs are bicrenulate, and the internal ribs converge toward, and become obsolescent at the middle of the valve. The body cavity is well removed from the ventral margin, and the large, rudely orbicular muscle impression lies a little in from the byssal area. Dimensions.— Holotype (G344a), right valve, height 43.8 mm.; width 47.9 mm.; thickness 16.5 mm. Paratype (J344b), right valve, height 30.9 mm.; width 32.9 mm.; thickness 11.1 mm. Paratype (1344c), right valve, height 27.3.; width 29.2 mm.; thickness 9.6 mm. Type locality.— Mare formation at W-14, on hillside above west bank of Quebrada Mare Abajo. One broken right valve, the holotype. Other localities.— Lower Mare formation at W-13, on hillside above west bank of Quebrada Mare Abajo. One right valve, a paratype. Lower Mare formation, in small stream 100 meters west of Quebrada Mare Abajo. One right valve, a paratype. Mare formation at W-25, south flank of Punta Gorda anticline. One large broken right valve. Comparisons.— P. caribeus, n, sp. is not to be confused with the preceding P. catianus, n. sp.; the latter is a smaller shell than P. caribeus, the dorsal margins diverge considerably less, and the concentric markings are much stronger on the interspaces and ribs alike. Other allied species are P. ventonensis Cooke (1919, pp. 130-131, pl. 12, figs. 1a, b) from what is stated to be the Oligocene of Cuba; P. aztecus Bose (1906, pp. 72-73, pl. 7, figs. 3-4) from the Pliocene of Mexico; P. soror urumaconis Harris (1927, pp. 22-23, pl. 13, fig. 1; pl. 14, figs. 3-4) from the Miocene of the State of Falcon, Venezuela; and P. soror codercola Harris (1927, pp. 23-24, pl. 13, fig. 3; pl. 14, figs. 1, 5; pl. 15, fig. 7) from the Miocene and Pliocene of Falcon. P. ventonensis has two ribs less, and they are flattened on top whereas those of P. caribeus are gently rounded. On P. aztecus the interspaces are a little narrower and the ribs a little broader than on the right valve of the Cabo Blanco shell; also, according to Bose's description, the right posterior ear of P. aztecus is marked only by fine concentric striae whereas there are radial riblets on both ears of P. caribeus. Both P. soror urumaconis and P. s. codercola have one or two more radial riblets on the auricles than does P. caribeus, n, sp.; furthermore, P. s. urumaconis is less fan-shaped and P. s. codercola more fan-shaped than P. caribeus from Cabo Blanco.» NORMAN EDWARD WEISBORD, 1964
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