Spondylus decoratus Nagao, 1934
NAGAO, T. 1934. Cretaceous Mollusca from the Miyako district, Honshû, Japan. Journal of the Faculty of Science, Hokkaido University [Series 4, Geology and Mineralogy], 2 (3): 177-277, pls. 23-39. [p. 210, pI. 27, figs. 2, 5-7]
1934 Spondylus decoratus Nagao, 1934
T. Nagao, 1934, plate 27.
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«Shell oval, slightly or fairly higher than Iong, a little oblique. Test thin.
Left valve regularly convex, with an evenly curved ventral margin; umbo moderately prominent, sometimes small, with the apical angle of about 100°, or in one case slightly smaller than 90°. Both ears distinct, narrow, smooth, with an obtuse outer margin. Surface covered by numerous, crowded, narrow, equal and more or Iess wavy radial ribs and slightly narrower shallow grooves in alternation. About seven ribs broader and more elevated than the interstitlal ribs which are about six or seven in number between each two broader ones. Broader ribs distinctly and coarsely spiny. Right valve usually flattish dorso-ventrally but evenly convex antero-posteriorly; surface of attachment sometimes large. Surface with numerous, crowded, narrow, subequal radial ribs and interstitial grooves, the latter usually almost equal in breadth to or slightly broader than the ribs themselves. Concentric lines and intermittent grooves also exist. Height Length (of the left valve)
Dimensions: 37 mm. ca. 35 mm. Localities and geological horizons: The Hiraiga Sandstone; Haipe, Hiraiga, Moshi and Hideshima. The Moshi Sandstone; Haipe. The Orbitolina Sandstone; Raga.
All the specimens are more or Iess weathered, so that it is almost impossible to know their perfect sculpture. In one of them, the left valve is provided with seven strong radial ribs which are somewhat broader and more elevated than the interstitial-ribs and ornamented with coarse prominent spines on top. In one of the other specimens, which is high, the stronger ribs are not prominent, only slightly surpussing the narrower ones in breadth.
The present species is similar in form and sculpture to S. roemeri DESH.[1] from the Neocomian of France and Germany and the Lower Greensand of England and S. gibbosus D'ORB.[2] from the Gault of France and England and the Gault and Aptian of Switzerland. The Japanese form, however, has the stronger ribs broader, more distinct and more regularly disposed and the, narrower ribs more crowded than in the first of these European species. It is also distinguished from the second of the latter by its less inflated left valve, with more prominent intermittent ribs. We have, moreover, another right valve (Pl. XXVII (V), Fig. 8) which is high, rather great in convexity, with a prominent umbo and covered all over by numerous concentric elevated lamellae, besides crowded narrow radial ribs. This specimen may belong to this same species in question and is similar in several points to one of the specimens of P. gibbosus figured by H. WOODS (PI. XX, Fig. 7) from England. S. dutempleanus D'ORB.[3] from the Upper Cretaceous of Europe is decidedly more convex and less oblique, with more crowded radial ribs than ours.» [1] A. D'ORBIGNY: Pal. Franç. Terr. Cret., Vol., III, 1847, p. 655, Pl. CCCCLI, figs. 1-6. F. J. PICTET and G. CAMPICHE : Foss. Terr. Crét. Ste. Croix, Op. cit., ser. 5, 1870, pp. 256, 260. A. WOLLEMAN: Die Biv. u. Gastrop. d. deutsch. u. hollännd. Neocom. Abhandl. d. k. preuss. geol. Landes., N. F. pt. 31, 1900, p. 20. H. WOODS: A Monogr. Cret. Lamell. England, Vol. I, 1901, p. 116, Pl. XX, figs. 4a-d.
[2] A. D'ORBIGNY: Pal. Franç. Terr. Crét. Op. cit., 1847, p. 658, Pl. CCCCLII, figs. 1-6. F. J. PICTET and W. ROUX : Moll. Foss. Grès verts de Genève, p. 514, Pl. XLVII, fig. 1 (?2) (S. brunneri). F. J. PICTET and E. RENEVIER : Foss. Terr. Aptien. Op. cit., ser. I, 1858, p.136 (S. brunneri). F. J. PICTET and G. CAMPICHE: Foss. Terr. Crét. Ste. Croix. Op. cit., ser. 5, 1870, p. 257, Pl. CLXXXII, figs. 1-4. H. WOODS: A Monogr. Cret. Lamell. England, Vol. I, p. 117, Pl. XX, figs. 5-11. [3] A.D'ORBIGNY: Pal. Franç. Terr. Crét., Vol. III, p. 672, Pl. CCCLX, figs. 6-11. F. J. PICTET and G. CAMPICHE: Foss. Terr. Crét. Ste. Croix. Op. cit., ser. 5, p. 262. E. HOLZAPFEL: Die Moll. d. Aachen. Kreide. Palaeontographica, Vol. XXXV, 1899, 244, Pl. XXVII, figs. 8-10. H. WOODS: A Monogr. Cret. Lamell. England, Vol. I, p. 125, Pl. XXII, figs. 11-14; Pl. XXIII, figs, 1-5. TAKUMI NAGAO, 1934
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«Observations and comparisons.— Many well preserved specimens exhibiting the external features of two valves are referable with certainty to Spondylus decoratus NAGAO, 1934, although the outline, ornamentation and width of attachment area vary considerably in the right valve. The difference in ornamentation of the two valves are seen also in NAGAO's syntypes and probably constitute a specific character. An imperfect right valve, which was figured by NAGAO (pI. 27, fig. 8) as Spondylus aff. decoratus, has many erect subconcentrie lamellae on its surface. Such lamellae are also well developed in some of the right valves at hand, and their prominence seems to be fairly variable in this species.
As stated by NAGAO (1934), the present species resembles Spondylus roemeri DESHAYES, 1842, from the Neocomian and Aptian, and Spondylus gibbosus D'ORBIGNY, 1847, from the Aptian of western Europe, in the outline of two valves. The radial ribs of these species are, however, not so clearly differentiated in two orders as those of the present species. The umbonal region is not so sharply pointed in S. roemeri, and the primary ribs of S. gibbosa are much weaker than in the present species. Spines are probably less developed in S. gibbosus. Several Cretaceous species with magnificient spines, such as Spondylus spinosus (SOWERBY, 1814) (non S. spinosus SCHREIBERS, 1793), are easily distinguishable from the present species by the subequivalve shell and simple radial ribs. Spondylus japonicus AMANO in AMANO and MARUI (1958) (non S. japonicus KURODA, 1932) is another Cretaceous spondyliid found in Japan, but it has much larger dimensions and its left valve is not spinose.» Occurrence.--Lower Miyakoan (Aptian). Dirty grey sandy shale of the 1st cycle of the Miyako group at loco Rn. 2065, Hideshima, Sakiyama, Miyako City, Iwate Prefecture. A boulder of calcareous sandstone from the northern coast of Moshi, Iwaizumi town, Shimohei County, Iwate Prefecture. NAGAO reported this species also from the Hiraiga formation at the south of Hiraiga, Tanohata village, the same county.»
HAYAMI, I. 1965. Lower Cretaceous marine pelecypods of Japan, part I. Memoirs of the Faculty of Sience, Kyushu University, [Serie D - Geology], 15 (2): 221-349, pls. 27-52. [p. 325, 326]
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Spondylus decoratus, Nagao; I. Hayami, 1965, Lower Cretaceous marine pelecypods of Japan, part I, plate 47, figures 4-9; plate 52, figure 6.
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