Chesapecten madisonius madisonius (Say, 1824)
SAY, T. 1824. An account of some of the fossil shells of Maryland. Journal of the Academy of Natural Sciences of Philadelphia, 4 (1): 124-155. [p. 134]
1824 Pecten madisonius Say, 1824
1862 Pecten edgecomensis Conrad, 1862
1875 Liropecten [sic] carolinensis Conrad in Kerr, 1875
1862 Pecten edgecomensis Conrad, 1862
1875 Liropecten [sic] carolinensis Conrad in Kerr, 1875
Pecten jeffersonius var. edgecombensis (Conrad); L. C. Glenn, 1904, The Systematic Paleontology, Miocene deposits of Maryland, plate 100, figure 3.
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«P. Madisonius. Much compressed, with about sixteen striated ribs.
DESCRIPTION. Shell rounded, much compressed; the whole surface covered with scaly striae: ribs elevated, rounded, with about three striae on the back of each; intervening grooves rather profound; ears equal, sinus of the ear of the superior valve profound, extending at least one third of the length of the ear. Length rather more than four inches and a half; breadth four inches and four-fifths. In magnitude this shell is justly entitled to compare with the preceding; but it differs in being much less convex, and in having a much more profound sinus in the ear of the superior valve. Three specimens, from which the above description was taken, belong to the Academy, and were presented by Mr. Watson.» THOMAS SAY, 1824
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«Discussion: Chesapecten madisonius is rare in the Goose Creek Limestone. The scant material present varies from 10 to 14 ribs. Gibson (1987) reported C. madisonius with similar low rib counts from the Lee Creek mine, Aurora, North Carolina. Typical specimens of C. madisonius from higher in the section have 16 to 22 ribs. This low rib-number morphology has been called Lyropecten carolinensis Conrad, 1873 (holotype in the Academy of Natural Sciences Philadelphia). Lyropecten carolinensis would become Chesapecten madisonius carolinensis (Conrad) if it proves to be a valid subspecies. It does not co-occur with typical C. madisonius. Too few specimens are presently available to resolve the question. Chesapecten septenarius and Chesapecten jeffersonius produced rare individuals with 10 to 12 ribs, but C. madisonius may be recognized by its narrower ribs and coarse radial threads with strong scaling.
CAMPBELL, M. R. & L. D. CAMPBELL. 1995. Preliminary Biostratigraphy and Molluscan Fauna of the Goose Creek Limestone of Eastern South Carolina.Tulane Studies in Geology and Paleontology, 27 (1-4): 53-100, pls. 1-5. [p. 78]
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Chesapecten madisonius (Say) subspecies? carolinensis (Conrad); M. R. Campbell & L. D. Campbell, 1995, Preliminary Biostratigraphy and Molluscan Fauna of the Goose Creek Limestone of Eastern South Carolina, plate 1, figure 2.
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«Occurrence.— The type locality is unknown but probably Virginia or North Carolina.
Additional Virginia localities (Yorktown Formation Zone 2 of Mansfield) include the York River from Yorktown (fig. 1, loc. 40 ; USGS loc. 25329) to 2 miles (3.2 km) below Yorktown (fig. 1, loc. 46; USGS loc. 25335), Cobham Wharf (fig. 1, loc. 42; USGS loc. 25336), Rices Pit (fig. 1, loc. 41; USGS loc. 25330), and Sycamore Bend (fig. 1, loc. 44; USGS loc. 25333). North Carolina localities (Yorktown Formation Zone 2 of Mansfield) include the rte. 258 bridge at Murfreesboro (6-9 ft (2+ m) above the Virginia St. Marys contact and Zone 2 Yorktown) (fig. 1, loc. 33; USGS loc. 25322), and Lee Creek Pit (fig. 1, loc. 45 ; USGS loc. 25334) . Comments.— The reasons for restricting the name Chesapecten madisonius to specimens found in Zone 2 of the Yorktown Formation are discussed in the section on C. nefrens. In Say's description of C. madisonius, he was probably considering as the superior valve the right valve, which in this genus, unlike many other Pectinidae, is the lower valve. The right valve does have a distinct sinus which is especially pronounced in younger individuals. Certainly, as Say was comparing the holotype of C. jeffersonius, the specimens of Pecten clintonius, and the holotype (monotype) of C. septenarius with the right valves of C. madisonius, he would have seen a pronounced sinus, which is about one-third the length of the ear in smaller individuals (pl. 7, fig.7). Although the three "striae" are usually more prominent in specimens of C. nefrens, the number of striae in the specimens we consider to be C. madisonius from the Yorktown Formation is usually three, particularly in specimens from certain beds. Say indicates in his description that the number of striae was not constant in the specimens before him. Such inconstancy would be normal for C. madisonius but unusual for a collection of specimens of C. nefrens. Also the term "striae" is hardly applicable to the scaly sculpture common in C. nefrens, whereas it is quite applicable to C. madisonius and particularly to the specimen here illustrated as the lectotype of C. madisonius (pl. 6, fig. 3, 4). In number of ribs both C. nefrens and C. madisonius are similar. Prior to this paper and before recognition of Say's specimen at the Philadelphia Academy, a worker at the British Museum had selected from Finch's collection a specimen which he considered making a lectotype of C. madisonius. The specimen he selected is a Yorktown Formation C. madisonius. This selection would indicate that the material in Finch's collection which most resembles the description of C. madisonius is a Virginia Yorktown specimen. Say states that C. madisonius has about 16 ribs. Our lectotype has 15 ribs, while the British Museum speciment (a right valve) has 16 ribs. Conrad applied Say's name madisonius to the Maryland species and consequently gave another species name, edgecombensis, to what was actually the P. madisonius of Say. All known references to C. madisonius in the Calvert and Choptank Formations are to the species here called nefrens and all known references to C. madisonius in the Yorktown Formation are misidentifications of the species formerly known as Pecten edgecombensis, here shown to be the madisonius of Say (1824). Dall (1898) incorrectly recorded the species (Pecten edgecombensis = C. madisonius) from Langley's Bluff, Md. Glenn (1904) incorrectly recorded this Yorktown species (P. edgecombensis) from the St. Marys River, Md., and also from Langley's Bluff, Md. Tucker-Rowland (1938) incorrectly recorded this species (P. edgecombensis) from Little Cove Point, Md. and her other "Maryland" locality (Grove Wharf) is in Virginia. There are no known occurrences of Chesapecten edgecombensis (= C. madisonius) in Maryland. Glenn's (1904) figured specimen (pl. C, fig. 3) of this species (P. edgecombensis) is wrongly labeled "St. Marys River" in the plate explanation. The specimen actually came from Edgecombe County, N.C., and was collected by J. L. Bridges and entered in the National Museum catalogue in 1863 (type locality and collection from which original specimens of edgecombensis came). Plate 6, figures 3 and 4 show the specimen which appears to be the only one remaining from the three original type specimens of Say's Pecten madisonius. It agrees with Say's original description in having three striae on the back of elevated ribs, in having equal ears, in the length and height measurements, and in being much more compressed than C. jeffersonius. This specimen was obtained from the Philadelphia Academy of Natural Sciences. Collections in the British Museum apparently lack the type specimens. Because the specimens of C. madisonius were not collected by Finch, they probably were not sent to England. Some small specimens of C. madisonius are found in the Finch collection. It should be noted that the specimen TuckerRowland (1938) figures (pl. 4, fig. 8) and mentions as the possible holotype of C. madisonius (Say, 1824) is actually a specimen collected in 1887 by Frank Burns from New Jersey (according to the U.S. Geological Survey Cenozoic Collection Catalogue).» WARD, L. W. & B. W. BLACKWELDER. 1975. Chesapecten, a new genus of Pectinidae (Mollusca: Bivalvia) from the Miocene and Pliocene of eastern North America. United States Geological Survey Professional Paper, 861: 1-24, pls. 1-7. [p. 17, 18]
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Chesapecten madisonius (Say); L. W. Ward & B. W. Blackwelder, 1975, Chesapecten, a new genus of Pectinidae, plate 6, figures 1-4; plate 7, figures 1, 7, 8.
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«Pecten edgecombensis CONRAD, Acad. Nat. Sci. Phila., Proc., 14: 291, 1862; HEILPRIN, op. cit., 33: 419, 1881.
Liropecten carolinensis CONRAD, in Kerr, Geol. N. Car., App.: 18, 1875. Pecten jeffersonius var. edgecombensis CONRAD, DALL, Wagner Free Inst. Sci., Trans., 3: 722, 1898; GLENN, Geol. Surv. Md., Miocene: 379, pl. 100, fig. 3, 1904. DESCRIPTION. — Conrad's original description:
"Suborbicular; height not quite equal to the length; lower valve-ribs 16 to 17, prominent, but not elevated, square or convex-depressed, not quite as wide as the intervening spaces, radiately lined with finely squamose striae, most conspicuous towards the margins, interstices of ribs carinated, in the middle squamose and finely striated; ears with fine close unequal squamose radiating lines, the larger ones most prominent on the posterior side; margins of ligament pit carinated." Fourteen to fifteen flat-topped ribs which are somewhat narrower than the interspaces. Usually five scaly, elevated threads on the summits of the ribs, the central one commonly the weakest. One strongly elevated, scaly cord in the center of each interspace, with a valiable number of scaly threads on either side. Sides of the ribs sculptured by weak, scaly threads. Submargins sculptured by close-set, scaly threads. Auricles subequal; scaly radial threads alternate in strength; sculpture of the byssal auricle slightly coarser. Small, inconspicuous fasciole. Young individuals have quite narrow, sharply elevated ribs, with narrow, channeled interspaces. Concentric sculpture of little elevated lamellae. Three scaly threads on the summits of the ribs. Valves tend to be oval in outline. Ctenolium of about 4 denticles. Larger specimens from Coggins Point, Va., have seven scaly threads on the summits of the ribs. The valve Conrad named carolinensis has 12 ribs; few traces of scaly threads in the interspaces; slightly convex; conspicuous byssal fasciole, slight sinus. The holotype is eroded almost, beyond recognition. The label, Academy of Natural Sciences of Philadelphia, gives no locality. Height 77, width 51 mm. DIMENSIONS. — Syntypes, both right valves: Height 87, width 77, convexity 17.5 mm.; height 90, width 78, convexity 16.5 mm. Hypotype, height 102.5, width 105 mm. LOCALITIES. — Tarboro, Edgecombe County, N. C. (type), (Conrad); Suffolk, and Petersburg, Va., (Dall); Little Cove Point, and Glove Wharf, Md.; Langleys Bluff, Md., (Glenn); Kingsmill, Gloucester Point, and Bellefield, Va. HORIZON. — St. Marys, and Yorktown (Miocene). HYPOTYPES. — Collection Cornell University. SYNTYPES. — Collection U. S. National Museum, Cat. Nº 2495.» 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. 16]
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Chlamys (Lyropecten) jeffersonius edgecombensis (Conrad); H. I. Tucker-Rowland, 1938, The Atlantic and Gulf Coast Tertiary Pectinidae of The United States, plate 2, figure 5; plate 4, figure 6.
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