Argopecten comparilis (Tuomey & Holmes, 1855)
TUOMEY, M. & F. S. HOLMES. 1855-1856. Pleiocene fossils of South
Carolina: containing descriptions and figures of the Polyparia, Echinodermata
and Mollusca. Russell and Jones, Charleston, South Carolina, xvi, 152 pp, pls.
1-30. [p. 29, pl. 11, figs. 6-10]
1855 Pecten comparilis Tuomey & Holmes, 1855
1932 Pecten (Plagioctenium) evergladensis Mansfield, 1932
1932 Chlamys (Plagiotecnium) comparilis jacksonensis Mansfield, 1932
1939 Pecten (Chlamys) caloosensis Mansfield, 1939
1932 Pecten (Plagioctenium) evergladensis Mansfield, 1932
1932 Chlamys (Plagiotecnium) comparilis jacksonensis Mansfield, 1932
1939 Pecten (Chlamys) caloosensis Mansfield, 1939
M. Tuomey & F. S. Holmes, 1855, plate 11.
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«P. testa orbiculata, aequivalvi, aequilaterali vel inaequilaterali; 23 costis convexis, concentrice striatis; auriculis subaequalibus.
DESCRIPTION. Shell orbicular, convex, somewhat thick, equivalve, with concentric lines of growth, ears nearly equal; lower valve, buccal ear notched, radiately and coarsely ribbed, with five to six ribs; anal ear ribs smaller and more numerous; upper valve, ears with the radiating lines equal; ribs and interstices nearly equal. This fossil is distinguished from P. EBOREUS by having the ribs more raised and convex, both valves more convex, and by the coarse ribs of the buccal ear of the lower valve. Like P. EBOREUS, it is also a variable shell, some specimens nearly equilateral, and others very inequilateral. It also bears a strong resemblance to a recent shell from the coast of Florida.
LOCALITY. Darlington; Smith's, Goose Creek».
MICHAEL TUOMEY & FRANCIS SIMMONS HOLMES, 1857
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«Comparison. A. comparilis differs from A. anteamplicostatus in having more numerous plicae (see text-fig. 7), with more closely spaced concentric lamellae, and an equiconvex or only slightly right-convex, rather than distinctly right-convex profile. Compared to A. vicenarius vicenarius, A. comparilis has a thinner shell, is less left-convex, and has higher and narrower right plicae.
Stratigraphic range. Upper Miocene (Ecphora and Cancellaria Faunizones, Tamiami Formation, Pinecrest Beds, Duplin Formation, and Yorktown Formation ). Geographic distribution and ecology. The species is widely distributed and is found in upper Miocene deposits in the Florida panhandle and peninsula and in South Carolina. A small number of specimens in the U.S. National Museum, correctly identified with A. comparilis, are from the Savannah River, Georgia (Duplin Formation), Nansemond River, Virginia (Yorktown Formation), and near Petersburg, Virginia (Yorktown Formation?). These areas in Georgia and Virginia were field-checked by the author and no A. comparilis were found, although A. eboreus is locally abundant. In exposures of the Yorktown Formation at Deep Creek, Virginia (locality 84), the author found only one valve of A. comparilis in an extensive pecten fauna containing A. eboreus and Lyropecten? jeffersonius. A. comparilis, therefore, is apparently rare north of Florida, except in the deposits of the Duplin Formation in Berkeley County, South Carolina. The South Carolina deposits, at localities referred to by Tuomey & Holmes ( 1857, p. xi, 29) as "Smith's, Goose Creek," and by Cooke (1936, p. 729) as "Yeamans Hall," were apparently exposed only in pits and can no longer be found. A. comparilis occurs in strata that also contain A. anteamplicostatus, considered here, on morphological grounds, to be a primitive bay scallop. The former also occurs in a variety of lithologies, such as the argillaceous, sandy shell marl of the Choctawhatchee Group at Jackson Bluff, Leon County, Florida, the quartz sands containing only calcitic shells in the Tamiami Formation in the Caloosahatchee River area, and the sandy limestones of the southern Florida Tamiami Trail region. The Jackson Bluff deposits were studied by Du Bar & Taylor (1962), who concluded that the sediments were deposited under open-marine conditions in depths from 5 to 20 fathoms. Puri & Vernon (1964, p.229) consider the Tamiami Formation of the southern Florida peninsula to have been deposited in an open-sea, inner-neritic environmerrt. Brooks et al. (1963, p.50), considered a more arenaceous phase of the Tamiami Formation in De Soto County, Florida, to represent a "deep, epineritic shelf environment with moderate to strong turbulence." Probably a whole complex of environments is represented by Tamialni deposits, from very shallow-water carbonate banks and bays to deeper water, openmarine conditions. For these reasons and because of its highly variable morphology, A. comparilis is considered to have been ecologically generalized, compared to living Atlantic ancl Gulf of Mexico species, and able to live both in the open waters of the continental shelf (including the shallow waters of carbonate banks) and in bays and sounds. Remarks on morphological variation. The above description and comparison are of representatives of A. comparilis that will be referred to as the high-ribbed ecotypes in the following section on comparative morphology and infraspecific variation (see tables 30, 31). These forms are best developed in the deposits of the Choctawhatchee Group at Jackson Bluff, Leon County, Florida, but also occur in the type area of the species in South Carolina and in the Tamiami Formation of the Caloosahatchee River area, including fossils that Mansfield (1939, p. 52) called Pecten caloosensis. Variants that form the other end of what appears to be a morphological continuum and that will be referred to later as the low-ribbed ecotypes (tables 32,33) occur in the Tamiami Formation of southern Florida in the area of the Tamiami Trail and the Everglades. Remarks on type specimens. Two right valves bearing the U.S. National Museum catalogue number 11447, from "Smith's, Goose Creek," Berkeley County, South Carolina, were designated by Mansfield (1939, p. 35) to replace the neotype designated by Rowland (1938, p. 43), which was from southern Florida and hence did not conform to Tuomey and Holmes' original locality for the species. Because Mansfield did not specify which of the two right valves was to be the neotype, the larger and more complete one is here so designated. The remaining right valve is recatalogued as USNM (P) 646012.» WALLER, T. R. 1969. The evolution of Argopecten gibbus stock (Mollusca: Bivalvia), with Emphasis on the Tertiary and Quaternary Species of Eastern North America. The Paleontological Society Memoir, 3 [Journal of Paleontology, 43 (5, supplement)]: 125 pp. [p. 53]
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Argopecten comparilis (Tuomey & Holmes); T. R. Waller, 1969, The evolution of Argopecten gibbus stock, plate 4, figures 9-12, 18, 19; plate 5, figures 1-11, 13.
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«The characters that separate C. comparilis from C. eborea, with which it has been commonly confused, are well illustrated in the original figures.
The species is restricted to a few localities at the top of the Miocene and the base of the Pliocene scattered from southern Virginia to Florida. In Florida C. comparilis has been recognized only in the Cancellaria zone. Distribution: The recorded distribution of Pecten comparilis Tuomey and Holmes (Pleiocene fossils of South Carolina, p. 29, pl. 11, figs. 6-10) is as follows: Yorktown formation at Petersburg and 16 miles below Suffolk, Nansemond River, Va., one specimen in the United States National Museum collected by the late Frank Burns from each locality; upper Miocene at Darlington, S. C. (Tuomey and Holmes); Pliocene at Goose Creek, S. C.; upper Miocene bed at Porters Landing on the Savannah River, Ga.; and upper Miocene (Cancellaria zone), Florida.— Mansfield, W. C., Jour. Paleontology, vol. 10, No. 3, p. 180, April 1936.»
GARDNER, J. 1943. Mollusca from the Miocene and lower Pliocene of Virginia and North Carolina. Part 1. Pelecypoda. United States Geological Survey Professional Paper, 199-A: 1-178, pls. 1-23. [p. 37]
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Chlamys (Aequipecten) comparilis (Tuomey and Holmes) Mansfield; J. Gardner, 1943, Mollusca from the Miocene and lower Pliocene of Virginia and North Carolina, plate 7, figures 2, 3, 4, 7.
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«REMARKS. — The Florida shells become conspicuously more inequilateral and heavier with age. Valves of adult specimens usually equally convex. Margins scalloped, resembling eboreus, s.s. auricles subequal; the right anterior with sculpture of coarse radial threads. Fasciole wide; notch small. Auricles of left valve, and right posterior auricle have from 5 to 8 fine radials. Adult valves, have no ctenolium. Provinculum present; auricular crura not conspicuous. Interior has broad ribs extending toward beak approximately one-third the height of the shell.
Valves of young individuals more convex than adults; radial and concentric sculpture similar. Young valves have larger auricles in proportion to size of shell than adult specimens. Ctenolium of 4 or 5 denticles present, Provinculum present, but more conspicuous in older shells. Since the types are evidently lost, I designate as neoholotype the figured right valve from Buckingham, Fla. DIMENSIONS. — Neoholotype, height 75, width 67 mm.; hypotype, height 47.5, width 41 mm. LOCALITIES. — Buckingham (left valve hypotype), Acline, Ft. Denaud (neoholotype), and Prairie Creek, Fla.; Walkers, N. C.; Harveys Creek, one-half mile above abandoned mill, Leon County, Fla., Mansfield; borrow pit near Jackson Bluff, Leon County, Fla., Mansfield; well 1 mile west of Holland post-office, Leon County, Fla., Mansfield; 2 miles north of Hosford, Liberty County, Fla., Mansfield; Gully Pond, and Hamlin Pond, Washington County. Fla., Mansfield; one-half mile east of Evans, Liberty County, Fla., Mansfield; one-half mile south of Knox Still Landing, Franklin County, Fla., Mansfield; Petersburg, and Nansemond River 16 miles below Suffolk, Va., Burns; Porters Landing, Savannah River, Georgia, Mansfield; Darlington, and Smiths on Goose Creek (type), S. C., Tuomey and Holmes. HORIZON. — Yorktown and Choctawhatchee (Miocene); Pliocene. HYPOTYPE. — Collection H. I. Tucker-Rowland. NEOHOLOTYPE. — Collection H. I. Tucker-Rowland.» TUCKER-ROWLAND, H. I. 1938. The Atlantic and Gulf Coast Tertiary Pectinidae of The United States. Section III Systematic Descriptions. Mémoires du Musée Royal D'Historie Naturelle de Belgique [2me Série], 13: 1-76, pls. 1-6. [p. 43, 44]
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Chlamys (Plagioctenium) comparalis (Tuomey and Holmes); H. I. Tucker-Rowland, 1938, The Atlantic and Gulf Coast Tertiary Pectinidae of The United States, plate 3, figure 11; plate 4, figure 14.
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