Chesapecten santamaria (Tucker-Rowland, 1934)
TUCKER-ROWLAND, H. I. 1934. Some Atlantic Coast Tertiary Pectinidae. The American Midland Naturalist, 15: 612-621, pls. 25-27 [Under H. I. Tucker]. [p. 615, pl. 26, fig. 2]
1934 Chlamys (Lyropecten) santamaria Tucker-Rowland, 1934
H. I. Tucker-Rowland, 1934,
plate 26. |
«Description. — Shell equilateral, suborbicular, inequivalved. Radial sculpture of 12 to 16, most commonly 12 to 14, brood, well elevated ribs which are approximately 4 mm. narrower, at the ventral margin, than the interspaces. Right valves commonly have about 12 ribs which an about 2 rnm. narrower than the imterspaces. The right valves are flat, or nearly so, and resemble C. madisonius Say very closely in outline; left valve convex in the umbonal region; auricles subequal, radial sculpture of fine, scaly threads, the anterior the more coarsely threaded; fasciole broad. Auricles of the left valve subequal, uniformly sculptured with fine scaly threads. Summits and sides of the ribs threaded with numerow fine, scaly threads. Interspaces similarly ornamented; one or two of the threads are usually more strongly developed, especially on the right valve. Submargins have a fine uniform sculpture of closely spaced, scaly threads. Interior ribbed to the umbones. Provinculum presen. Ctenolium retained throughout the life of the individual. Dimensions: right valve, height, 130, width 126 mm. (figured shell); left, height 120, width 115 mm.; convexity 33.5 mm.
Remarks. — This species has the characteristic sculpture of C. jeffersonius Say and in outline closely resembles C. madisonius Say. It is separated from jeffersonius by the deep byssal notch, longer right anterior auricle, retention of the ctenolium in adult valves. It differs from madisonius in its finer, more uniform, scabrous sculpture; broader, flatter ribs, shorter byssal auricle. It is possible that this species may be related to both madisonius and jeffersonius. C. madisonius occurs first in the Cbipola Miocene, while C. jeffersonius, s.s., appears in the lower Yorktown. The stronger development of some of the inrercostals and the shortening of the byssal auricle suggest a possible relationship through edgecombensis. Occurrence — St. Mary's Miocene. St. Marys Rivet, Md. (type); Chancellor Pt. and Langleys Bluff, Md.; Snow Hill, Green County, N. C. Cotypes. — Right valve, collection Paleontological Research Institution, Ithaca, New York. Left valve, United States National Museum, Cat. No. 2498. The valves are from the same locality. Paratype. — A right valve, United States National Museum, Cat. No, 2498. Dimensions: Height 101, width 79 mm. An imperfect shell.» HELEN lONE TUCKER-ROWLAND, 1934
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«Discussion.— Chesapecten santamaria differs from C. middlesexensis middlesexensis in having a less inflated right valve, a deeper byssal notch, broader, flatter ribs, less coarse subradials on the ribs, longer retention of the ctenolium, and a shorter hinge area. It is reasonably clear that C. santamaria is a member of a lineage that can be traced back to C. nefrens (upper Calvert and Choptank Formations) and whose immediate progenitors can be found in the St. Marys Formation at Langleys Bluff and at Little Cove Point. Chesapecten santamaria is found only in the "Windmill Point beds" of the St. Marys Formation. The first Chesapecten species to appear in the Claremont Manor Member of the Eastover Formation, C. middlesexensis middlesexensis, bears little resemblance to C. santamaria, indicating a considerable loss of record or a population shift, or both.
Type information.— Lectotype: USNM 193448, selected by Ward and Blackwelder (1975) (pararype of Tucker, 1934). Type locality: St. Marys River, Md. Figured specimen.— Right valve (USNM 405198), a topotype specimen from 0.5 km above Windmill Point, right bank of the St. Marys River, St. Marys County, Md. (locality 12). Collected by Thor Hansen, then a student at George Washington University. Stratigraphic and geographic range.— St. Marys Formation, Windmill Point beds (lower upper Miocene) in Maryland and Virginia.» WARD, L. W. 1992. Molluscan bioestratigraphy of the Miocene, middle Atlantic Coastal Plain of North America. Memoirs of the Virginia Museum of Natural History, 2: 1-159. [p. 70]
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Chesapecten (Chesapecten) santamaria (Tucker, 1934); L. W. Ward, 1992, Molluscan bioestratigraphy of the Miocene, middle Atlantic Coastal Plain of North America, plate 7, figure 4.
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«Occurrence.— Original type locality was given as the St. Marys River, Md. As a reference locality in the type area we designate the tan shell bed (3 ft (1m) above high tide) in the St. Marys Formation at Windmill Point, St. Marys River, St. Marys County, Md. (fig. 1, loc. 12; USGS loc. 25304). This locality is probably the source of the type material.
Additional reference localities (in the St. Marys Formation of Shattuck 1904) are Essex Mill, Va. (fig. 1, loc. 13; USGS loc. 25058), White Oak Landing, Va. (fig. 1, loc. 14; USGS loc. 25059), and Mantua Landing, Va. (fig. 1, loc. 15; USGS loc. 25061). Comparison and remarks.— Chesapecten santamaria differs from C. rniddlesexensis in having a less inflated right valve, a deeper byssal notch, flatter ribs which are squared off, less coarse subradials on the ribs, longer retention of the ctenolium, and a shorter hinge area. Contrary to Tucker's description, the plicae in C. santamaria are not usully narrower than the interspaces but subequal and slightly variable in proportion from specimen to specimen. Also specimens from Langleys Bluff do not appear to be the same species but rather are intermediate between C. santamaria and C. nefrens. Tucker's (1934) measurements in the description of this species are incorrect. In naming C. santamaria, Tucker (1934) designates two specimens as cotypes and one specimen as a paratype. The cotype specimen, which was figured, was stated to be in the collection of the Paleontological Research Institution, Ithaca, N.Y. However, it is apparently not there (Brann and Kent, 1960). The other cotype (a left valve) and the paratype (a right valve) are figured in this paper. This right valve was in Tucker's possession at the time the original species was described (Tucker, 1934, p. 615), the locality description for this specimen is more exact than that given for the other specimens, and, as the right valve is most distinctive of this species, this valve is designated the lectotype. Cotypes are highly artificial categories. According to present practice, the three specimens would have syntypic status. The selection of an unfigured "syntype" as lectotype was necessitated by the uncertainty of the depository of the originally figured specimen. This right valve which is designated the lectotype agrees quite well with the details from the figure of Tucker's original specimen. The left-valve cotype of Tucker (USNM 2498) was collected by E. Ruffin in 1863 from St. Marys River, Md. The right-valve paratype of Tucker (USNM 193448) was collected by Harris in 1891 from the St. Marys River, Md., along the eastern bank for perhaps 0.5 mile (0.8 km) above the mouth of St. Inigos Creek. Many of the larger specimens collected were float on the beach (USGS 1oc. 2342).» 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. 12]
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Chesapecten santamaria (Tucker); L. W. Ward & B. W. Blackwelder, 1975, Chesapecten, a new genus of Pectinidae, plate 4, figures 3-6.
Chesapecten santamaria (Tucker); L. W. Ward & B. W. Blackwelder, 1975, Chesapecten, a new genus of Pectinidae, plate 7, figures 5, 12.
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