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Volume 1990 (1990)
- Issue 160 Pages 609-
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Volume 1990, Issue 160
Displaying 1-5 of 5 articles from this issue
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EIJI TAGUCHI1990 Volume 1990 Issue 160 Pages 609-617
Published: December 30, 1990
Released on J-STAGE: May 25, 2010
JOURNAL FREE ACCESSAn interesting new cardiid belonging to the genus Vepricardium was discovered from a mudstone of the Middle Miocene Yoshino Formation of the Katsuta Group in Okayama Prefecture, southwest Japan. This species, Vepricardium (Vepricardium) okamotoi, sp. nov., is described herein, and its average relative growth is examined. Judging from the mode of occurrence, lithofacies and associated forms, this species must have lived in a muddy bottom in the inner sublittoral zone, and is regarded as an indicator of a tropical marine environment at that time.View full abstractDownload PDF (1222K) -
TATSURO MATSUMOTO1990 Volume 1990 Issue 160 Pages 618-630
Published: December 30, 1990
Released on J-STAGE: May 25, 2010
JOURNAL FREE ACCESSA peculiar ammonite recently acquired by Masatoshi Kera from the Coniacian rock of the Masago-zawa in the Yubari Mountains, central Hokkaido, is described as a new species. It may represent the earliest species of Eupachydiscus Spath, 1922, retaining some features which characterize certain species of Tongoboryceras Housa, 1967. In this connexion Tongoboryceras is redefined so that it may include comprehensively more species. Also Menabonites Housa, 1967 is reviewed with a proposal to include it in Pseudojacobites Spath, 1922 in a revised sense. In the available material there is no significant difference of size, i. e. a microconch versus macroconch relationship, between bior trituberculate species of Pseudojacobites and 'normal' pachydiscid species of Tongoboryceras, although the two genera are closely allied to each other.View full abstractDownload PDF (1825K) -
KAZUSHIGE TANABE1990 Volume 1990 Issue 160 Pages 631-640
Published: December 30, 1990
Released on J-STAGE: May 25, 2010
JOURNAL FREE ACCESSEarly life history of two species of Limopsis, L. (Crenulilimopsis) oblonga (A. Adams) and L. (Limopsis) azumana Yokoyama is discussed on the basis of well-preserved Middle Pleistocene juvenile specimens from the southwestern Kanto region, central Japan. L. (C.) oblonga has a relatively large prodissoconch I (Pd I) (ca. 180 μm in length) and a well-marked prodissoconch II (Pd II), suggesting lecithotrophic development with a short pelagic stage. L. (L.) azumana, in contrast, probably underwent direct development or ovoviviparity because of its unusually large prodissoconch (ca. 400μm in length) without Pd II stage. The two species exhibit a similar pattern in hinge development : the hinge in the full-grown prodissoconchs is made of a long, uninterrupted series of ligamental pits (provinculum), and anterior and posterior cardinal teeth appear at the early dissoconch stage, increasing their number as the shell grows. Predominance of minute shells at the fossil locality strongly suggests an extremely high juvenile mortality in the two species.View full abstractDownload PDF (2322K) -
SEIICHIRO MATSUI1990 Volume 1990 Issue 160 Pages 641-662
Published: December 30, 1990
Released on J-STAGE: May 25, 2010
JOURNAL FREE ACCESSSeven major groups of molluscan associations are recognized in the Japanese cold water molluscan faunas ranging over about 5 million years from latest Miocene to Pleistocene. Each of the groups is composed of local associations which are similar not only in species or genus composition but also in environmental preference to one another, and accordingly are in ecologically parallel relationships with one another. The distribution of the association groups was controlled primarily by water depth and grain size of bottom sediments. Each of the fossil association groups has analogous living communities comparable in their composition and habitat around Japan. Among these seven groups the Acila-Turritella Association Group is the most prevalent and is the fossil representative of the lower sublittoral community. The Delectopecten and Nuculana Association Groups are interpreted as deeper dwellers. The Anadara and Macoma-Mya Association Groups represent shallow marine environments, comparable with sandy and muddy upper sublittoral faunas, respectively. Occurrence of the Thyasira Association Group may be related to a reducing environment. The Chlamys Association Group occupied coarsegrained sand bottoms of the lower sublittoral or upper bathyal zone.View full abstractDownload PDF (3542K) -
KUNITERU MATSUMARU1990 Volume 1990 Issue 160 Pages 663-673
Published: December 30, 1990
Released on J-STAGE: May 25, 2010
JOURNAL FREE ACCESSThis paper deals with the description and illustration of a new genus of the trematophorate miliolids (Fabulariidae), Neolacazopsis osozawai, n. gen., n. sp., from the basaltic and calcareous sandstone of the Eocene Setogawa Group, at Ashikubo-Okugumi, Shizuoka City and at Hasama, Okabe-Cho, both of Shizuoka Prefecture, Japan.View full abstractDownload PDF (4539K)
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