Chasapecten middlesexensis (Mansfield, 1936)
MANSFIELD, W. C. 1936. Stratigraphic significance of Miocene, Pliocene and Pleistocene Pectinidae in the Southeastern United States. Journal of Paleontology, 10 (3): 168-192, pls. 22, 23. [p. 187, pl. 22, fig. 5, 6]
1936 Pecten (Chlamys) santamaria middlesexensis Mansfield, 1936
1938 Chlamys (Lyropecten) madisonius richardsi Tucker-Rowland, 1938
1938 Chlamys (Lyropecten) madisonius richardsi Tucker-Rowland, 1938
W. C. Mansfield, 1936, plate 22.
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«Pecten santamaria middlesexensis is like santamaria Tucker, s.s., in its major features, but differs in the following minor features. Right valve slightly more inflated, the ears relatively wider, the byssal notch shallower, the ribs less rounded distally; Ieft valve with less rounded ribs distally and coarser subradials on the ribs. The new subspecies is a descendant of P. santamaria.
Dimensions of syntypes (U. S. Nat. Mus. 373074): Right valve, length, 140 mm.; height, 130 mm.; convexity, 18 mm. Left valve, length, 154 mm.; height, 140 mm.; convexity, 30 mm. The specimens figured by me (19c) as Pecten madisonius Say variety, have shallower channels between the ribs than the syntypes of P. santamaria middlesexensis, but in other features are the same and are considered only mutations of this subspecies. However, these specimens occur in the highest beds of the St. Marys formation of Virginia. Type locality: Station 3915, Urbanna, Middlesex County, Virginia. Horizon: St. Marys formation, zone 2 (Crassatellites meridionalis zone).» WENDELL CLAY MANSFIELD, 1936
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«Discussion. — Chesapecten middlesexensis middlesexensis differs from C. jeffersonius in having more ribs, thinner valves, less inflated valves (especially the right valve), less tight closure along the ventral commissure, a deeper byssal notch, a byssal fasciole which is differentiated from the auricle with respect to sculpture and elevation, and the exterior of the valves covered with moderately coarse scabrous lirae.
Conrad (1863a, p.291) described a pectinid from the Miocene of Virginia and named it Pecten fraternus. The diagnosis of this specimen sounds very much like that of Chesapecten middlesexensis middlesexensis, but there is no figure, no locality other than Virginia, the type specimen appears to be lost, and the description is not complete enough to make a satisfactory judgment as to the intended taxon. Pecten fraternus is therefore considered to be a nomen dubium. Pecten tricarinatus Conrad (1867) may have been described from the same specimen Conrad used to describe P. fraternus Conrad (Heilprin, 1881), but again the identity of the taxon is unclear. Pecten tricarinatus is also considered to be a nomen dubium. Chesapecten middlesexensis middlesexensis is most abundant in the Cobham Bay Member of the Eastover Formation, but is present throughout the Eastover Formation. Type information.— Lectotype: USNM 373074 (Ward and Blackwelder, 1975). Type locality: The river front at Urbanna, Middlesex County, Va., "between the mouth of lUrbanna] Creek and Wharf of Weems line of Steamers on the Rappahannock River, Va." Figured specimen.— Right valve, a topotype specimen (USNM 258363), from Urbanna Creek, Middlesex County, Va. (USGS locality 25309). Stratigraphic and geographic range.— Eastover Formation (upper Miocene) of Virginia and North Carolina. Most abundant in the Cobham Bay Member of the Eastover. Specimens have been found as far south as the Neuse River in North Carolina.» 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. 69]
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Chesapecten (Chesapecten) middlesexensis (Mansfield, 1936); L. W. Ward, 1992, Molluscan bioestratigraphy of the Miocene, middle Atlantic Coastal Plain of North America, plate 2, figure 2.
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«Occurrence.— The type locality is Urbanna, Middlesex County, Va. in the lower Virginia St. Marys Formation (of Mansfield, 1936) (fig. 1, loc. 16; USGS loc. 3915).
Reference localities in the Virginia St. Marys Formation include the Nomini Cliffs (fig. 1, loc. 17; USGS loc. 25306), Hull Creek (fig. 1, loc. 18; USGS 25307), Bowlers Wharf (fig. 1, loc. 19; USGS loc. 25308) ; Urbanna Creek (fig. 1, loc. 20; USGS loc. 25309), Freeport (fig. 1, loc. 21; USGS loc. 25310), Blands Wharf (fig. 1, loc. 22; USGS loc. 25311), White Oak Landing (fig. 1, loc. 14), Court House Landing (fig. 1, loc. 23; USGS loc. 25312), Corbin Pond (fig. 1, loc. 24; USGS loc. 25313), Gressitt Pond (fig. 1, loc. 25; USGS loc. 25314), White Landing (fig. 1, loc. 26; USGS loc. 25315), Romancoke (fig. 1, loc. 27; USGS loc. 25316), the lower greengray sandy clay bed from Chippokes Creek (fig. 1, loc. 28) to Cobham Bay (fig. 1, loc. 29; USGS loc. 25318), the tan sandy shell bed (upper Virginia St. Marys Formation) from Sunken Marsh Creek (fig. 1, loc. 30; USGS loc. 25319) to Cobham Bay, the Nottoway River at 631 bridge (fig. 1, loc. 31; USGS loc. 25320), Murfreesboro (lower foot of section) (fig. 1, loc. 32; USGS loc. 25321), and ~ miles (3.2 km) above rte. 258 bridge at Murfreesboro (lower 2 ft (0.5 m) of section) (fig. 1, loc. 33; USGS loc. 25322). Comparison and remarks.— Chesapecten middlesexensis differs from C. jeffersonius in having more ribs, thinner valves, less inflated valves (especially the right valve) , less t; ght closure along the ventral commissure, a deeper byssal notch, a byssal fasciole which is differentiated from the auricle with respect to sculpture and elevation, and the exterior of the valves covered with moderately coarse scabrous lirae. Conrad (1862, p. 291) describes a pecten from the Miocene of Virginia and names it Pecten fraternus. The diagnosis of this specimen sounds very much like that of Chesapecten middlesexensis, but there is no figure, no locality other than Virginia, the type specimen appears to be lost, and the description is not complete enough to make a satisfactory judgement as to the intended species. Pecten tricarinatus Conrad (1867) may have been described from the same specimen Conrad used to describe P. fraternus Conrad (Heilprin, 1881). The type specimens of Chesapecten middlesexensis were collected by Frank Burns in 1903 from the river front at Urbanna, Middlesex County, Va., "between the mouth of Creek and Wharf of 'Veems line of Steamers on the Rappahannock River, Va." The right valve (USNM 373074) is here designated the lectotype of C. middlesexensis. The type specimens of Chlamys madisonius richardsi Tucker-Rowland (1938) are the specimens Mansfield (1928) illustrated as Pecten madisonius var. Although Mansfield (1936) thought these specimens represented a form occurring in the highest beds of the St. Marys Formation of Virginia, the specimens actually came from units which belong to the lower Virginia St. Marys Formation.» 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. 13]
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Chesapecten middlesexensis (Mansfield); L. W. Ward & B. W. Blackwelder, 1975, Chesapecten, a new genus of Pectinidae, plate 5, figures 1, 2 (above); plate 7, figures 4, 11 (below).
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