Camptonectes bubonis (Stephenson, 1941)
STEPHENSON, L. W. 1941. The larger invertebrate fossils of the Navarro Group of Texas. University of Texas Publication, 4101: 1-641, pls. 1-95. [p. 131, pl. 21, figs. 3-6]
1941 Pecten (Camptonectes) bubonis Stephenson, 1941
L. W. Stephenson, 1941, plate 21.
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?1916. Pecten argillensis Conrad. Gardner, Maryland Geol. Survey, Upper Cretaceous (2 vols.), p. 588, pl. 34, figs. 3-5.
«Shell thin, subcircular in outline, subequilateral, subequivalve, depressed convex. Beaks small, direct, depressed, scarcely projecting above the hinge line, situated at about the midlength of the shell. Hinge straight, more than half as long as the shell, with 1 or 2 long, parallel crural ridges which interlock on opposite valves, and a deep central, triangular resilifer in each valve. The anterior ear of the right valve is longer than the posterior one and is separated from the main body of the shell by a deep anterior byssal notch, and by a narrow, deep channel which extends from the notch to the hinge margin at the beak; anterior ear of left valve a little larger than the posterior one; each of the four ears sharply separated from the main body of the shell by a radiating sulcus; these sulci diverge from the beak at an angle of about 96 degrees, and are slightly concave upward in their trend away from the beak. The surface is ornamented with numerous, crowded, nearly flat-topped, low, radiating bifurcating ribs which are separated by much narrower, sharp depressions; the ribs are somewhat irregular in their trend, and quite irregular in their width, which averages less than 0.5 mm., and rarely exceeds that amount; the ribs on the ears are similar to those on the body of the shell, though in general somewhat more irregular, and those on the anterior ears are finer. The surface exhibits fine concentric growth lines, but a few remnants indicate that in addition to these the surface originally possessed thin, concentric lamellae spaced 0.5 to 2 mm. apart, which outwardly curved downward, touching the shell, thus forming round-crested, crenulated ridges, the crenulations corresponding to the radiating ribs (see pl. 21, fig. 5); on most shells practically no evidence remains of the former existence of these ridges.
Dimensions of the holotype, a right valve from Mississippi shown in plate, 21, figure 3: Length 27 mm., height 27 mm., convexity about 4 mm. Because of their fine state of preservation shells from the Owl Creek formation at Owl Creek, 2½ miles northeast of Ripley, Tippah County, Mississippi, are selected as types. The Texas shells are scarcely distinguishable from the Mississippi ones, though the ribbing averages a little finer. Pecten (Camptonectes) argillensis Conrad, [178] the type of which came from somewhere in Tippah County, Mississippi, is a much smoother shell, as described and illustrated, and has a much wider angle of divergence at the beak; the whereabouts of the type is unknown. Pecten (Camptonectes) bellisculptus Conrad, which several authors have regarded as synonomous with P. argillensis, is a distinct species characterized by fine distinct radiating sculpture all over the surface. The shell from the lower part of the Ripley formation at Coon Creek, Tennessee, which Wade referred incorrectly to P. argillensis, exhibits much finer sculpture than that of the present species, and in this respect is more like P. bellisculptus Conrad. The shell described by Gardner from the Monmouth formation of Maryland under the name P. argillensis Conrad, is like P. bubonis except that the radiating ribs are more subdued, producing a smoother surface. Pecten virgatus Nilsson, [179] from the Cenomanian of France, and Pecten (Camptonectes) curvatus Geinitz, [180] from the Cenomanian of England, are closely related species. Types.— Holotype, a right valve from the Owl Creek formation, Owl Creek, 2½, miles northeast of Ripley, Mississippi, U.S.N.M. no. 76432; 2 figured paratypes, U.S.N.M. no. 76433; 5 selected unfigured paratypes, U.S.N.M. no. 76434; 1 example from Texas, U.S.N.M. no. 76435. Distribution in Texas. — Navarro group, Corsicana marl: About 5 miles east by north of Greenville (12924); about 4 miles east-northeast of Greenville (10886); ½ mile below Martindale (7621, 15526, 15527); 1 3/10 miles north of McQueeney (7637, 1 specimen figured; 15524) ;1 3/10 miles southeast of Marion (13389). Navarro group, Kemp clay: Near Deatsville (764); ?near old Garfield (7603); 1½ miles northwest of Texas Hill,Travis County (15533); 2 7/8 miles west southwest of Staples (10878); west of Zuehl (7085); 4/5 mile north of Zuehl (16489). Navarro group, Escondido formation: Questionably on eastward-facing slope of Medina River valley, 2 miles below (?)» [178] Conrad, T. A., Acad. Nat. Sci. Philadelphia Jour., 2d ser., vol. 4, p. 283, pl. 47, fig. 3, 1860. (See Amer. Jour. Sci., vol. 5, p. 99, 1869.)
[179] D'Orbigny, Alcide, Paléontologie Francaise, Terrain Crétacé, vol. 3, p. 602, pl. 431, figs. 7-10, 1843-1847. [189] Woods, Henry, A monograph of the Cretaceous Lamellibranchia of England, vol. 1, p. 159, pl. 29, figs. 7a, b, and pl. 37, fig. 16, 1904. LLOYD WILLIAM STEPHENSON, 1941
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