Euvola jamaicensis Waller, 2011
WALLER, T. R. 2011. Neogene Paleontology of the Northern Dominican Republic. 24. Propeamussiidae and Pectinidae (Mollusca: Bivalvia: Pectinoidea) of the Cibao Valley. Bulletins of American Paleontology, 381: 1-197 [p. 101, pl. 13, figs. 11-14; pl. 14, figs. 1-2]
T. R. Waller, 2011, plates 13, 14.
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«Pecten (Pecten) barretti Woodring, 1925: 62, pl. 7, figs 6-7, not P. barretti Seeley, 1861: 118, pl. 6, fig. 1, Cretaceous of England.
Pecten ventonensis Cooke. Mongin, 1968: 476, pl. 40, fig. 1 (not of Cooke, 1919). Original description.— "Shell large; dorsal margins slightly concave, diverging at an angle of ca. 95º; right valve strongly inflated, sculptured with 19-22 high, almost square ribs, their edges and tops slightly rounded, separated by narrower, deeply channeled interspaces; in the interspaces and on the flanks of the ribs are obscure, fine, slightly raised concentric lamellae; left valve slightly concave, sculptured with the same number of narrower square ribs, and deep, flat interspaces of the same width or slightly wider; concentric lamellae more prominent than on right valve and occasionally extending across ribs, but less conspicuous on ribs than in interspaces; submargins relatively wide and forming a deep ledge on left valve; auricles subequal, sculptured with weak radial ribs and fine concentric lamellae; interior ventral margin deeply fluted" (Woodring, 1925: 62). Description.— Shell of small to moderate size, known to reach ca. 45 mm Ht, acline, equilateral, L exceeding Ht, moderately flaring, umbonal angle increasing during ontogeny to ca. 110º; RV cvx moderate to high, reaching ca. 33% Ht; LV slightly concave with raised shoulders; disk gapes not observed, probably narrow if present. Disk of RV with 22-23 ribs decreasing gradually in amplitude toward disk flanks, commonly twice as wide as interspaces, crests smooth except for very shallow radial troughs and beading of very low relief present on some ribs late in ontogeny, sides of ribs vertical to slightly undercut; commarginals well developed in interspaces, passing nearly straight across interspaces and up sides of ribs but ending abruptly adjacent to overhanging rib crests; disk of LV with 23-25 ribs, those on shoulders finer, lower, and more closely spaced than others, those of central sector somewhat narrower than interspaces in width, crests slightly flattened, sides steeply sloping, with barely perceptible medial radial troughs on crests developing in late ontogeny; commarginal lamellae well developed in interspaces, passing straight across ribs in early ontogeny, weakly present across ribs in some specimens in late ontogeny. Disk flanks of both valves low, moderately steep, and curved in cross section, with closely spaced commarginal growth lines but lacking radial costae. Auricles approximately equal in length; right anterior auricle with persistent shallow byssal notch, byssal fasciole raised, separated from anterior disk flank by sharp groove, active ctenolium disappearing in late ontogeny; surface of right anterior auricle with 3 or 4 radial costae in central sector, anterior margin of auricle rounded, sloping dorsally toward beak; right posterior auricle with posterior margin shallowly sigmoidal, bearing 4 or 5 moderately strong radial costae in central part, separated by deep groove from posterior disk flank; left anterior auricle with nearly straight anterior margin forming slightly obtuse angle with dorsal margin; left posterior auricle with posterior margin slightly outwardly convex, meeting dorsal margin with slightly more obtuse angle than that of anterior auricle; both left auricles with radial costae variable in number and distribution, ranging from 5 or 6 moderately strong costae distributed over entire width of auricles to fewer costae developed in dorsal part of auricle but weak or absent ventrally. Hinge dentition of RV with narrow dorsal tooth and sharply raised resilial tooth on each side of resilifer, intermediate teeth absent, hinge plate bearing vertical microcrenulations. Interior surface of RV with foliated-calcite re-entry extending only to approximately mid-adductor-scar level; re-entry on LV nearly completely covering area inside pallial line except for muscle scars. Edges of ribs on shell interior carinate near valve margins; ribs extending slightly inward from pallial line, then becoming covered by inner shell layer. Etymology.— From Jamaica. Holotype and measurements.— USNM 352776, 1 RV, 29.8 mm Ht, 32.2 mm L. Type locality.— USGS Locality 2580: "Bowden Formation at Bowden, on the east side of Port Morant, in the parish of St. Thomas, lying on the south coast of Jamaica near its eastern end" (Woodring, 1925: 7). Other material.— Jamaica: Bowden Formation, 5 LV from locality USGS 2580 in addition to the holotype, and 1 RV, 3 LV from the same locality in the collections of the University of California Museum of Paleontology (UCMP 556136-556138, 556140); August Town Formation, 1 RV, 1 partial LV in Smithsonian collections from "Vertical beds near 8 mile Windward Road, August Town Series." Dominican Republic: NMB 15830, Mao Formation on Río Gurabo, 807-810 m above base of section, 1 RV; NMB 16885, Mao Formation on Río Cana, 1,177 m above base of section, 1 RV, 1 partial LV; USGS 8663, Province of Santiago, Arroyo Las Lavas, crossing of road from Santiago to Monte Cristi, 1 RV fragment. Puerto Rico: USGS 8654, unnamed formation on south side of Vieques, 3 RV, 3 LV, and fragments; USGS 17953, upper member of Camuy Formation, northern Puerto Rico, 3 RV, 9 LV. Remarks.— Hertlein (1936: 6) was the first to discover that Pecten (Pecten) barretti Woodring, 1925, is a primary junior homonym of Pecten barretti Seeley, 1861, a species from the Cretaceous Upper Greensand of England. Hertlein, however, did not rename Woodring's species because he regarded it as a junior synonym of Pecten (Pecten) ventonensis Cooke, 1919, described from the La Cruz Formation in the Santiago area of southern Cuba, a synonymy that Woodring (1928: 61) had suspected. Unfortunately both of these species are known from rather meager material, but because of morphological differences described in the comparisons that follow, it is advisable to keep these taxa separate. The junior homonym therefore requires a new name, introduced herein as Euvola jamaicensis n. n. The new description of Euvola jamaicensis n. n. is based on specimens from both the Bowden and August Town Formations of Jamaica at the localities listed above. The left valve paratype figured by Woodring (1925: pl. 7, fig. 7) is unusual in comparison to the other left valves in having 5 strong radial auricular costae bordered ventrally by a barely visible costa, these distributed across the dorsal two-thirds of the surface of both auricles. The auricular costae on the other left valves are weaker, fewer in number, and more concentrated in the dorsal region of the auricular surface (Pl. 14, Fig. 2, UCMP 556140). All of these left valves resemble one another in being rather thick-shelled and only slightly concave and in having similar patterns of smaller ribs clustered on the disk shoulders. A second right valve and a partial left valve from Jamaica, not mentioned by Woodring (1925) but labeled by him as being from the "August Town series," are from "vertical beds near 8 mile, Windward Road, 10 March 1944," collector unknown. They are part of a lot consisting of large Hyotissa haitensis (G. B. Sowerby I, 1850) and Spondylus bostrychites Guppy, 1867, a small lophinine oyster, molds of a Conus, and an unidentified heterodont bivalve. The right valve of Euvola in this lot (Pl. 14, Fig. 1) is important, because it expands the morphological concept of E. jamaicensis n. n. It is larger than the holotype (47 mm Ht, compared to 30 mm), but like the holotype, its posterior auricle bears strong radial costae separated by a deep groove from the posterior disk flank. It has one more disk rib than the holotype but the same pattern of a single smaller lateralmost rib on each side and the same rib profile with slightly undercut rib flanks and commarginal lamellae ending abruptly at the overhang before reaching the rib crest. The left-valve fragment from the August Town locality is comparable to the left valves of E. jamaicensis n. n. from the Bowden shell bed. The right valve from the Mao Formation on the Río Cana (NMB 16885) in the Dominican Republic (Pl. 13, Figs 11-13) matches the holotype in valve outline, rib count, rib pattern, and number and pattern of auricular costae, but is more convex. Comparisons.— Euvola jamaicensis n. n. closely resembles E. caribea (Weisbord, 1964) from the late Pliocene Mare Formation and Pleistocene Cumaná Formation of Venezuela (see Gibson-Smith, 1976: 4, regarding the age of the Mare Formation). The Venezuelan species, however, is much larger (reaching at least 85 mm Ht), has stronger auricular costae, particularly on the right anterior auricle, has higher shoulders and steeper disk flanks on its left valve, and has a much more extensive foliated-calcite re-entry on its right valve, reaching below the level of the ventral margin of the adductor scar. Weisbord (1964) had only right valves of Pecten (Pecten) caribeus and only left valves of a second species that he next described as Pecten (Pecten) maiquetiensis. Articulated specimens that I collected in the Cabo Blanco area of Venezuela prove that the latter is a junior synonym of the former. Euvola jamaicensis n. n. differs from E. ventonensis in having a thicker shell, relatively more convex right valve, relatively broader right disk ribs, and more auricular costae, particularly on the right posterior auricle. Compared to extant E. raveneli (Dall, 1898), E. jamaicensis n. n. has rib interspaces on the right valve that are narrower relative to width of ribs and that have much more prominent commarginal lamellae. Furthermore, E. raveneli has two or three strong dorsal costae on its left auricles, whereas in E. jamaicensis n. n., these are weaker and more variable in number and position, and the rib crests of E. raveneli bear much more prominent medial grooves in late ontogeny. Evolution.— Euvola jamaicensis n. n. essentially fills a morphological gap between earlier (Miocene) Euvola that had weak or absent auricular costae and relatively less convex right valves and later species that developed, beginning in the late Pliocene, greater differential convexity of valves and stronger left dorsal auricular costae. Occurrence.— In the northern Dominican Republic, Euvola jamaicensis n. n. is the stratigraphically highest occurring pectinid in the combined collections made by the NMB team and the Vokeses. It is known only from the upper Mao Formation. Distribution.—Outside the Dominican Republic, Euvola jamaicensis n. n. is known from the Bowden and August Town formations of Jamaica, the upper member of the Camuy Formation of Puerto Rico, an unnamed formation on Vieques Island, and an unnamed formation in Guadeloupe. All of these occurrences are Pliocene and probably not older than middle Pliocene.» THOMAS RICHARD WALLER, 2011
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