Chlamys (Leptopecten) desultoria Weisbord, 1964
WEISBORD, N. E. 1964. Late Cenozoic Pelecypods from Northern Venezuela. Bulletins of American Paleontology, 45 (204): 1-564, pls. 1-59. [p. 145, pl. 15, figs. 3-6]
«Chlamys (Leptopecten) desultoria, new species PI. 15, figs. 3-6
The following description pertains to the right valve. Shell small, thin, subcompressed to slightly inflated, nearly equilateral, the dorsal margins low, diverging at an angle of 94 to 98 degrees, the ventral margin rounded. Beak about level with hinge line, the hinge line straight. Auricles unequal, the anterior one slightly longer, subrectangular, and with a prominent byssal notch, the posterior one triangular. Separating the anterior auricle from the disk is a prominent, wedge-shaped, fasciolar sulcus, widening rather rapidly away from the beak. Anterior ear sculptured by five or six small unequal riblets which are crossed by concentric lamellae, the lamellae crowded and low near the beak, more widely spaced and a little higher toward the extermity; posterior ear marked by five or six fine radial riblets crossed by concentric threads which are more pronounced in the decussated interspaces. The radial riblets of both ears vary somewhat in size and spacing from specimen to specimen. Ctenolium bearing four or five teeth. Disk sculptured by 13 to 15 radial ribs separated by interspaces about equally as wide. In the interspaces near the base at the middle area of the valve there is a single feeble intercostal thread usually situated submedially in the interspaces but occasionally to the side. The ribs are moderately high and subsquarish, and some of them may be faintly divided. The concentric markings consist typically of rather widely spaced laminae which are generally much sharper in the interspaces; on unweathered specimens it may be seen that the laminae in ascending the sides of the ribs form small vaulted arches, although they straighten out on the summit of the ribs where they are usually smoothed off; on the paratype (J342a), the concentric laminae are worn away on both the ribs and interspaces on the lower half of the valve, thus modifying the appearance of the ribs. The submargins may or may not bear a faint radial groove, and the concentric lineations there are relatively inconspicuous, particularly on the anterior submargin. Within the valve, the ligamental groove is long, narrow, and shallow, and is finely scored by numerous short vermicular grooves. Chondrophore small, triangular. Both ears are shallowly and broadly fluted, the flutings longer on the anterior ear. Internal ribs strong, extending far upward in the valve, generally depressed or sulcate in greater or less degree along the middle, and separated by fairly deep interspaces. Dimensions.— Holotype (G342a), right valve, height 10.3 mm.; width 10.3 mm.; thickness 1.1 mm. Paratype (J342a), right valve, height 9.6 mm.; width 9.8 mm.; thickness 2 mm. Paratype (G341a), right valve, height 11.4 mm.; width 12.3 mm.; thickness 1.9 mm. Type locality.— Mare formation at G-14, on hillside above west bank of Quebrada Mare Abajo. Two right valves, the holotype and a paratype (G341a). Other localities.— Lower Mare formation at G-13, on hillside above west bank of Quebrada Mare Abajo. Two right valves, one of them (J342a) a paratype. Lower Mare formation, in small stream 100 meters west of Quebrada Mare Abajo. One broken right valve. Comparisons.— The nearest related species from the Atlantic- Caribbean side of the Americas are Chlamys (Plagioctenium) irremotis Olsson and Harbison (1953, p. 56, pl. 3, figs. 7, 7a) from the upper Miocene and Pliocene of Florida, and Pecten (Aequipecten) effossus Brown and Pilsbry (1911, pp. 364-365, pl. 28, figs. 4, 6) from the middle Miocene of the Isthmus of Panamá. Both of these species differ from C. desultoria, n. sp. in lacking the minor radial thread in the intercostal areas, and C. effossa not only has several more ribs than the Venezuelan shell, but on the type of C. effosa the ribs are sharply tripartite. Other somewhat similar species from the Caribbean area are Pecten vaughani Cooke ( 1919, p. 133, pl. 8, figs. 2-4) from the lower Miocene of Anguilla; Pecten vaughani flabellum Cooke (1919, p. 134, pl. 8, figs. 6a, 6b, 7) from the reported Oligocene of Cuba; Pecten atlanticola Anderson (1929, pp. 156-157, pl. 19, figs. 2-3) from the middle Miocene of Colombia; and Pecten maturensis Maury (1925, p. 241, pl. 14, figs. 3-4) from the Matura Pliocene of Trinidad. All of the above may be distinguished from C. desultoria in lacking radial threads on the right anterior ear. In west America, analogous forms are Pecten woodringi Spieker (1922, Johns Hopkins Univ., Studies in Geol., No. 3, p. 125, pl. 7, figs. 4-5) from the middle Miocene of Peru and Ecuador (see Marks, 1951, Bull. Amer. Paleont., vol. 33, No. 139, pp. 331-332, pl. 3, fig. 1); Pecten (Chlamys) bellilamellatus Arnold (1906, p. 41, pl. 41, figs. 6, 6a, 7, 7a) from the Pliocene of California; the Pleistocene and Recent Pecten tumbezensis d'Orbigny (1846, Voyage Amer. Merid., vol. 5, p. 663); and the Recent Pecten palmeri Dall (1897, Nautilus, vol. 1, No. 8, p. 85) known only from the Gulf of California. On C. woodringi the radial threads on the right anterior ear are wanting or obsolete. C. bellilamellata is slightly more oblique than C. desultoria, and lacks the minor radial thread in the intercostal spaces. C. tumbezensis (see Grau, 1959, pp. 118-120, pl. 40), living from the Gulf of California to Peru in waters just below tide to 70 fathoms, is somewhat oblique whereas C. desultoria is nearly equilateral. On C. palmeri (see Grau. 1959, pp. 113-114, pl. 36), a species found on rocks and on sandy or muddy bottoms to 50 fathoms, the primary ribs are longitudinally threaded whereas on C. desultoria the primary ribs are simple.» NORMAN EDWARD WEISBORD, 1964
|
N. E. Weisbord, 1964, plate 15.
|