Leptopecten? auroraensis Ward & Blackwelder, 1987
WARD, L. W. & B. W. BLACKWELDER. 1987. Late Pliocene and Early Pleistocene Mollusca from the James City and Chowan Rives Formations at Lee Creek Mine. In: Geology and Paleontology of the Lee Creek Mine, North Carolina, II, C. E. Ray (ed.), Smithsonian Contributions to Paleobiology, 61: 113-283, pls. 1-47. [p. 140, pl. 5, figs. 4-6]
Leptopecten? auroraensis, new species
PLATE 5: FIGURES 4-6 DIAGNOSIS.—Shell small, about 13 mm long, left valve only slightly convex, right valve quite convex, outline of disk slightly produced posteriorly. Byssal notch deep, ctenolium present, resilial insertion located anteriorly and in line with anterodorsal margin of disk. Resilial insertion of about equal length and height. Interior calcification in right valve heavy and obscuring fluting of the ribs. Auricular denticles and cardinal crura prominent. About 15 major plicae in right valve with very small ribs in interspaces (small ribs arising about 5 mm from the beak). Major plicae in right valve and sharply arched to narrowly rectangular, with spaces between major plicae about twice the width of the plicae; faint trace of concentric lamellae in interspaces.
Left valve with about 5 high, prominent ribs having sharply arched summits, and with 2 lower, broader, flattopped ribs between each of the 5 prominent ribs. A single faint fbld occasionally occurs between ribs. Concentric lamellae cover parts of the high ribs and the auricles. DISCUSSION.— Leptopecten leonensis (Mansfield, 1932: 58, type locality Ecphora Zone at Jackson Bluff, Florida) differs from L. auroraensis in that it has stronger auricular denticles, fewer ribs (10 as opposed to about 14 in L. auroraensis), which are covered by raised concentric lamellae and are almost V-shaped in cross-section. The cross-section of ribs of L. auroraensis is quite rounded in the right valve. The leflt valve of L. leonensis lacks the square-shaped, very flattened ribs seen between the V-shaped ribs of L. auroraensis. All the ribs of the type specimen of L. leonensis (a left valve) are V-shaped with one small V-shaped rib between each major rib while L. auroraensis has 2 flat ribs between each major rib. Also L. auroraensis has almost twice as many plicae on the auricles as does L. leonensis. Specimens from the Tamiami Formation are probably Leptopecten wendelli (Tucker, 1934). Tucker's (1934: 612) type locality is Fort Denaud where there is a good deal of spoil material from both the Tamiami Formation and from the Caloosahatchee Formation. Leptopecten is rare in the Caloosahatchee Formation, and Tucker's specimens apparently came from the Tamiami Formation. Leptopecten wendelli olgensis (Mansfield, 1939) is also probably from the Tamiami Forrnation and so too is Leptopecten irremotis (Olsson and Harbison, 1953) (See page 133 concerning collections used in Olsson and Harbison, 1953). Leptopecten wendelli is believed to be a senior synonym of L. Ieonensis. ln addition, L. wendelli olgensis probably represents only a variation within this species. Specimens of L. wendelli from Punta Gorda (Tamiami Formation, Florida, Cenozoic, USGS 22454) are almost twice the size of L. auroraensis. Similar-sized right valves of L. wendelli are very close morphologically to L. auroraensis, but the right valves have only half the convexity of Lee Creek specimens, and the auricular denticles are smaller than those in Lee Creek specimens. Tucker (1936, pl. 4, fig. 9) illustrated a specimen from Walkers Bluff, but it is only a left valve, and convexity measurements are not given for this specimen. Leptopecten sp. (unnamed) from the Chipola Formation at Ten Mile Creek, Florida (1 mile (1.6 km) west of Baileys Ferry), is an early representative of this group and is small (approximately 8.0 mm in height). The ribs tend to be about equal in size, except for minor alternation of rib size, and ribs on both valves are high and sharply arched. Concentric lamellae cover the exterior of both valves. The outline of the disk is produced posteriorly, and the auricles are similar to those of later members of this group. The Holocene species Leptopecten bavayi (Dautzenberg, 1900) from the West Indies has more numerous ribs in the right valve than does L. auroraensis. Leptopecten bavayi also has less tendency to alternate rib size (i.e., it has more uniform ribbing). Both valves of this Holocene species have one small rib between major ribs. The left valve of L. auroraensis has only a trace of these small ribs, the disk is less rounded in outline (the angle from the beak to the edges of the disk is lower), and the interior shows heavier calcification and a larger resilial insertion area. The right valve of L. auroraensis has stronger auricular dentricles and is slightly more convex than L. bavayi. The entire surface of L. bavayi is covered by concentric lamellae. The type species of Leptopecten is a West Coast species with a strongly inclined shape and as far as we know it does not alternate rib sizes. Atlantic species assigned to Leptopecten have probably been separate long enough and show enough difference to be considered a separate genus. FIGURED SPECIMENS.— Holotype, USNM 203898, USGS 25357 (Plate 5: figure 4). Paratype, USNM 203899, USGS 25357 (Plate 5: figures 5, 6). OCCURRENCE.— This species is rare at section 5 units B, C, and E. It occurs in 1 (E), 2 (B, D, E), and 6 (C). TYPE LOCALITY.-Clewiston, Florida (Caloosaharchee Formation). LAUCK W. WARD & BLAKE W. BLACKWELDER
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L. W. Ward, & B. W. Blackwelder, 1987, plate 5.
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