Eburneopecten clarkeanus (Aldrich, 1895)
ALDRICH, T. H. 1895. New or little known Tertiary
Mollusca from Alabama and Texas. Bulletins of American Paleontology, 1 (2): 55-82., pls. 1-5. [p. 68, pl. 5, fig. 11]
1895 Pecten clarkeanus Aldrich, 1895
T. H. Aldrich, 1895, plate 5.
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«Shell orbicular compressed; ears nearly equal; beaks pointed; both valves about equal, the right one convex, the umbones more slightly convex, the apex of valves smoother very minutely striated the lower and older part strongly marked with about 48 radiating ribs, strongest on the right valve, anterior ear on right valve with a sinus, ears striated.
Locality.— Sowilpa Cr., Ala. Geological horizon. Lisbon beds. This species combines the characters of two subgenera. The ribs in some specimens are quite plain near the beaks, then become obsolete and suddenly reappear below, where they often bifurcate. Examined under a glass, the ribs appear to be smooth and rounded; on the left valve the beaks are ribbed, but on the right they appear to be smooth. Young specimens are difficult to distinguish from P. scintillatus Conrad.» TRUMAN HEMINWAY ALDRICH, 1895
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«In the present study, the tribe Eburneopectinini is limited to the genus Eburneopecten because of morphological and stratigraphic evidence that this genus evolved from coarsely ribbed Dhondtichlamys in the early to mid-Eocene of eastern North America and is phylogenetically independent of so-called "Eburneopecten" in Europe (Fig. 1.2, Node E1 compared to A6). Well-preserved specimens of E. scintillatus consistently display fine radial costellae on the left beak that are ontogenetically decoupled from later costae that may appear near the ventral margin. The species retains costae throughout ontogeny on its right anterior auricle, whereas the costae on other auricles are absent or limited to early ontogeny. Similar decoupling of ribbing occurs within the range of variation of two older species that resemble E. scintillatus, and they are included here in Eburneopecten. One of these is E. clarkeanus (Aldrich, 1895) from the Cook Mountain Formation of Alabama of Bartonian age; the other is E. burlesonensis (Harris, 1919) from the Weches Formation of Texas of middle Lutetian age. The latter, older species resembles Dhondtichlamys in having strong steep-sided plicae but differs in having much finer antimarginal microsculpture in the rib interspaces. Both of these species exhibit great variation in the degree of rib interruption, with some specimens approaching the nearly smooth condition of Eburneopecten scintillatus. (See illustrations of these species in Harris 1919, pI. 14, figs. 11-13 and pI. 15, figs. 8-13.)»
WALLER, T. R. 2006. New Phylogenies of the Pectinidae (Mollusca: Bivalvia): reconciling Morphological and Molecular Approaches. In: S.E. Shumway & G.J. Parsons (Ed.), 2006: Scallops: Biology, Ecology and Aquaculture, 1-44, figs. 1.1-1.4. [p. 14, 15]
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Figure 1.2. A phylogeny of the six tribes of the subfamily Palliolinae.
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«This is a remarkably interesting and variable species as Aldrich has already pointed out. The vast number of young or small forms show the beautifully fine and distinct radiation about the umbo though with but slight traces of radiate sculpturing over the general surface of the shell (figs. 10, 12). Camptonectes marking is, however, well defined. Occasionally the radiate sculpturing expands and lengthens and covers the entire surface of the shell (figs. 8, 13). Again it appears about the margins only (fig. 9.) The shell substance is thin, and as Aldrich remarks, recalls P. scintillatus. At the type locality only, Sowilpa Cr., have we observed (in specimens kindly loaned by Aldrich) the particular form of ribbing shown on pl. 6, vol. 1 of these Bulletins. (See also pl. 15, fig. 8, of the present work). Even these specimens are not so thick and solid looking as the figure perhaps suggests. This fact has doubtless led Dall to consider a much more rugged form from the Brazos River, Tex., as true clarkeanus (Trans. Wag. Ill, 739, '98).
Not unfrequently valves of this species show a faint, broad, quinque-costate structure (see figs. 10 and 11). Small specimens of this species in the Academy Collection are labelled P. frontalis Dall. This name Dall gave to take the place of P. rogersi Clark which was pre-occupied. (See Trans. Wag., pp. 731 and 753). Of the equivalency of this Virginia form and others from the Jackson of Miss, we cannot speak with authority. Clark noticed his lapsus and renamed his rogersi, P. dalli, though just after Dall had proposed the name frontalis. The Va. forms are doubtless closely allied to clarkeanus, but Aldrich's name has three years priority over Dall's and Clark's. Type.— Aldrich Coll. Johns Hopkins Univ. Coll. Horizon.— St. Maurice Eocene. Specimens figured.— C. U. Coll. Localities.— Sowilpa Cr. in type form (figs. 8 and 9). At Hamilton Bluff and Lisbon often in abundance as small, almost smooth, very thin and scintillatus-like specimens, though sometimes large and smooth or sometimes with evident costation.» HARRIS, G. D. 1919. Pelecypoda of the St. Maurice and Claiborne Stages. Bulletins of American Paleontology, 6 (31): 5-268, pls. pls. 1-59. [p. 25, 26]
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Pecten clarkeanus Aldrich; G. D. Harris, 1919, Pelecypoda of the St. Maurice and Claiborne Stages, plate 15, figures 8-13.
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