"Chlamys" membranosus (Morton, 1833)
MORTON, S. G. 1833. Supplement to the "Synopsis of the organic remains of the ferruginous sand formation of the United States" [II]. The American Journal of Science and Arts, 24: 128-250, pls. 9, 10. [p. 130, pl. 10, fig. 4]
1833 Pecten membranosus Morton, 1833
1875 Pecten carolinensis Conrad in Kerr, 1875
1875 Pecten carolinensis Conrad in Kerr, 1875
«The Comfort Member is Claibornian (late middle Eocene) in age and is equivalent to the Gosport Sand of Alabama. Pecten membranosus Morton, found both in the Santee Limestone and the Comfort, is a senior synonym of Pecten wautubbeanus Dall found in the Claibornian of Alabama. Also common are Pecten clarkeanus Aldrich and Crassatella alta Conrad, both found only in Claibornian beds in Alabama.»
WARD, L. W., D. R. LAWRENCE & B. W. BLACKWELDER. 1978. Stratigraphic revision of the middle Eocene, Oligocene, and lower Miocene - Atlantic Coastal Plain of North Carolina. Geological Survey Bulletin, 1457-F: 1-23, figs. 1-3. [p. 9]
|
«Morton describes this species as "orbicular, convex, somewhat gibbous in the center, with about 80 distinct costae, the alternate ones being smaller." Dall has compared the types of Pecten carolinensis Conrad with that of P. membranosus Morton, and there is no doubt of their identity. Conrad's brief description is therefore quoted here:
Shell ovate, convex, ribs numerous, narrow, densely and minutely crenulated, rounded, alternating with two smaller interstitial radii which are also crenulated.
P. membranosus is one of the most abundant and characteristic fossils of the Castle Hayne marl. It is very widespread and as a rule is perfectly preserved. A more critical description of it will therefore be of value.
Shell suborbicular, slightly oblique, moderately convex, with nearly equal valves and from 22 to 35 primary radial ribs alternating with two secondary ribs, more or less strongly developed; submargins finely ribbed. Primary and secondary ribs bear coarse and closely spaced imbrications. Anterior ears longer ana sculptured with four or five coarse imbricated radiating ribs; posterior ears with finer radiating ribs; byssal notch of moderate depth; ctenolium present. Interior of valves snlooth, with margin slightly beveled; muscle scar high and slightly posterior. Dimensions of left valve: Height, 32.5 millimeters; breadth, 34 millimeters; depth, 6 millimeters. Localities: Wilmington and 3½ miles northwest of Wrightsboro, New Hanover County; Old Rocky Point quarry, Castle Hayne quarry, Northeast Cape Fear River 3½ miles above Castle Hayne Bridge, 3 miles northeast of Maple Hill, and 1 mile southwest of Maple Hill, Pender County; 5 miles east of Beulaville, 1½ miles northeast of Rose Hill, 2 miles south of Magnolia, and 5 miles west of Pink Hill, Duplin County; 4 miles south of Richlands, 1 mile southeast of Richlands, and 1½ miles southeast of Richlands, Onslow County; 2½ miles west of Dover, Jones County; 3 miles east of Quinerly, Craven County. Geologic horizon: Castle Hayne marl, of Jackson Eocene age.» KELLUM, L. B. 1926. Paleontology and stratigraphy of the Castle Hayne and Trent marls in North Carolina. United States Geological Survey Professional Paper, 143: 56 pp., 11 pls. [p. 19]
|
«P. (Chlamys) wahtubbeanus Dall, Trans. Wag. &c, 1898, vol. 3, p. 736, pl. 34, fig. 9.
Dall's original description.—Shell small, fiattish, with small, unequal ears and rounded disk; fourteen or fifteen ribs carrying basally three densely finely imbricated, rounded threads, the interspaces narrower with two crenulate threads; submargins with close, fine, imbricate threads; ears prominent, with a deep wide, byssal notch, radiately imbricate with coarse elevated radial threads; interior with shallow sulci, the cardinal crura developed but no lirae on the disk. Alt. 22, lat. 22 mm.
This species differs from the Claibornian* P. deshaycsii Lea by its threaded and less individualized ribs, its similarly sculptured valves, more conspicuous notch, and concentric sculpture and smaller size when adult. * Note that on p. 738, Trans. Wag. Ill no Pectens are known from the Claiborne sand.
We have emended the spelling of this species, the "h" having crept into the name from bad orthograpy of the collector. Dall states that this species is "abundant at Wautubbee." Our collections furnish many fine specimens from Wautubbee, but we scarcely feel like giving it the wide geologic range implied in "Claibornian and Jacksonian of Louisiana, Alabama and Mississippi."
This species is extremely variable in appearance, even at the type locality. The right valve seems to be far more abundant and is flatter than the left and is more apt to assume a worn appearance (see fig. 1). While the ribs, abotit the periphery in the right valve, nearly always show the tri-partite markings described by Dall, such secondary ornamentation on the left valve are far less conspicuous though present on the lower margin of the shell (see fig. 3). On the type specimen, however, such markings are well defined. Whenever the middle one of the three riblets is strongest, then, whether the rib be worn or intact, it apears narrow. Whenever the lateral riblets are well developed the rib has a broad appearance and the interspaces seem narrow and deep. In extreme cases the riblets are not distinctly developed but the imbricate lines of growth are well defined. The general aspect of the shell is accordingly greatly changed. Quite often, however, after a very marked growth line, the tri-partite ornamentation reappears. A very gibbose, perhaps somewhat pathologic specimen in our collection from near Negreet P. O., La. shows this feature in a remarkable degree. The broad ribbed variety we have named cainei, see below. Also see fig. 8, type of variety. From the sellaeformis, light-colored layers near the base of the bluff at Claiborne thin, varietal forms are found, one of which herewith figured (fig. 5) is quite as large as the average deshayesi from the sends above. It is characterized by the scaly spinosity of the bipartite ribbing shown on valves of willcoxi Dall (fig. 6), and described also as deshaysei var. tirmus by de Gregorio. The intimate relationship of some forms of deshayesi and wautubbeanus may also be noted by the fact that the usual small right valves generally known as lyelli, in the collection of the U. S. Nat. Mus. , No. 116,012, are classed as wautubbeanus. Type.— U. S. Nat. Museum. Horizon.— St. Maurice Eocene. Specimens figured.— Wautubbee and Hickory, Miss. var.; fig. 5 from base of bluff at Claiborne. Localities.— Simpkins place, 3 mls S. E. of Negreet, and St. Maurice, La; Wautubbee, Hickory, 8 mls W. of Enterprise, Miss.; 3 mls S. W. of Orangeburg, S. C.; Coffeeville, base of bluff at Claiborne, Ala.» 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. 22, 23]
|
Pecten wautubbeanus Dall; G. H. Harris, 1919, Pelecypoda of the St. Maurice and Claiborne Stages, plate 14, figures 1-4.
|
«Pecten membranosus Morton, Org. Rem., p. 59, pl. 10, fig. 4, 1834.
Pecten carolinensis Conr., Kerr, Rep. Geol. N. Car., App., p. 18, pl. 3, fig. 2, 1875; not Lyropecten carolinensis Conr., 1875. Eocene of Jones County, Haldeman; of Rocky Point and Wilmington, North Carolina, Stanton; Eutaw Springs, South Carolina, Conrad.
This somewhat resembles the recent P. ornatus Lam., but is shorter and more orbicular. There is no question of the identity of Mr. Conrad's P. carolinensis with Morton's species; I have compared the types.» DALL, W. H. 1898. Contributions to the Tertiary fauna of Florida. Silex Beds of Tampa and the Pliocene Beds of the Caloosahatchie River. Part IV. I. Prionodesmacea: Nucula to Julia. 2. Teleodesmacea: Teredo to Ervilia. Transactions of the Wagner Free Institute of Science of Philadelphia, 3 (4): viii, 571-947 p., pls. 23-35 (pls. 36 and 37 in part 5, 1900). [p. 736]
|