赤石山地の厚歯二枚貝(1新種)

概要

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The pachyodont pelecypods are the rare group of fossils in Japan, although Praecaprotina yaegashii(YEHARA) and Toucasia carinata(MATH.) were reported from Miyako and Hokkaido, respectively. Then the species described is a first discovery through the Central and West Japan. Pachytraga japonica OKUBO is based upon three left valves found in the block of black muddy limestone, while the right valves are not yet obtained. Diagnosis of this new species is as follows : Surface of the left valves generally smooth, except for several coarse radial ribs in the central portion. Umbo moderately produced. Anterior cardinal tooth strong, but the posterior reduced. Anterior accesory cavity well defined and divided into several chamberlets at the deep portion. The present species resembling to P. paradoxa PAQUTER from the Barremian or Aptian, is associated with such hexacorals as Montastrea? sp. and Thamnasteria cfr. yuraensis Euurnr, besides hippuritids fragments. In order to restore the valves consolidated in mother rocks, the senior writer used the method by which STORMER studied the trilobite morphology.
地学団体研究会の論文
1959-04-30