Transactions and proceedings of the Paleontological Society of Japan. New series
Online ISSN : 2186-0963
Print ISSN : 0031-0204
ISSN-L : 0031-0204
Volume 1994, Issue 176
Displaying 1-6 of 6 articles from this issue
  • YUKIO YANAGISAWA
    1994 Volume 1994 Issue 176 Pages 591-617
    Published: December 30, 1994
    Released on J-STAGE: May 25, 2010
    JOURNAL FREE ACCESS
    A new marine fossil araphid diatom genus Koizumia is established to receive three species, Koizumia tatsunokuchiensis (Koizumi) Yanagisawa comb. nov. (originally described as Rhaphoneis tatsunokuchiensis by Koizumi, 1972), K. adaroi (Azpeitia) Yanagisawa comb. nov. (originally described as Cymatosira adaroi by Azpeitia, 1911), and K. akibae Yanagisawa sp. nov. Detailed morphologies of the genus are presented with its precise stratigraphic and geographic distributions. The genus is characterized by cribrum-like siliceous layers across the pores of marginal ridge, the suture line on the marginal ridge and the presence of transapical and longitudinal rows of areolae on the valve face. The three features are unique to the genus and have never been observed in its related genera Rossiella Desikachary et Maheshwari and Bogorovia Jouse. Koizumia is typically neritic in distribution mainly in near-shore or upwelling regions of the middle latitudes, and is significantly different from Rossiella and Bogorovia, both of which have essentially an oceanic and tropical to subtropical distribution. Both the morphological uniqueness and the differing geographic distribution pattern are considered to be distinctive enough to form the basis of a new generic erection of Koizumia. The genus has a rimoportula in the pattern of "one per cell" with an apical pore field at each apex, and forms a long colony chain connected by marginal ridges. These features suggest that the genus can be placed in the family Cymatosiraceae Hasle, von Stosch et Syvertsen.
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  • FUMIO KOBAYASHI
    1994 Volume 1994 Issue 176 Pages 618-637
    Published: December 30, 1994
    Released on J-STAGE: May 25, 2010
    JOURNAL FREE ACCESS
    Sixty-five species referable to 36 genera of Carboniferous foraminifers are discriminated from the exotic limestone blocks embedded in the Jurassic accretionary complexes of the Itsukaichi district, southern Kanto Mountains. These foraminifers are Eostaffella, Profusulinella, and many others which have not yet been described in the Kanto Mountains. Endothyra igoi, Eostaffella kamiyozawensis, Profusulinella hinodensis and Pseudoendothyra musashiensis are newly proposed herein.
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  • MICHIAKI YUMOTO
    1994 Volume 1994 Issue 176 Pages 638-649
    Published: December 30, 1994
    Released on J-STAGE: May 25, 2010
    JOURNAL FREE ACCESS
    The development of carapace shell structure during ontogeny of Xestoleberis hanaii Ishizaki, 1968 was investigated with the aid of a scanning electron microscope (SEM). Photographs of broken sections of carapaces ranging from the second instar (the adult-7 instar) to adult reveal that the carapace is composed of four distinct layers : 1) an organic fibrous layer that is characterized by a network of organic fibers with few calcite grains ; 2) a foliated layer formed by an aggregation of plate-like grains ; 3) a granular layer consisting of an aggregation of granular grains ; and 4) a prismatic layer constructed of an aggregation of columnar grains extending perpendicularly to the valve surface. Three of the layers, i. e., all but the organic fibrous layer, are distinguished by the shape and arrangement of calcite grains. The calcified procuticle of adult specimens is composed of an outer organic fibrous, a middle granular, and an inner prismatic layer. That of juvenile specimens in the second to fourth instars consists of only the foliated layer. That of juvenile specimens in the fifth and sixth instars develops outer granular and inner prismatic layers. The seventh and eighth instar juveniles possess a procuticle of the same three layers as in the adult. During growth, the shell structure of this species thus undergoes a change in its constructional design between molt stages, particularly from fourth instar to fifth instar and from sixth instar to seventh instar.
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  • YOSHIO YUKI
    1994 Volume 1994 Issue 176 Pages 650-660
    Published: December 30, 1994
    Released on J-STAGE: May 25, 2010
    JOURNAL FREE ACCESS
    The gear-like intricate dentition of the Trigoniidae appears to fix the axis of valve opening and closing movement, while the opening and closing forces must be generated independently by the ligament and adductor muscles. As a result of experiments and moment analysis on living specimens of Neotrigonia margaritacea (Lamarck), it was found that the three axes determined by dentition, ligament and adductor muscles are largely different from one another in orientation. Provided that minimum friction is required for the smooth hinge movement, the opening force by ligament and closing force by adductor muscles have to compensate each other, and the axis of their resultant force may coincide with the dentition axis. The relatively short ligament in trigoniids seems to enable such a remote valve movement axis from the postero-dorsal margin as well as the formation of remarkably pennate shells like Pterotrigonia.
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  • KAZUTAKA AMANO
    1994 Volume 1994 Issue 176 Pages 661-676
    Published: December 30, 1994
    Released on J-STAGE: May 25, 2010
    JOURNAL FREE ACCESS
    Many specimens of Chlamys were obtained from the Early Pliocene Ogikubo Formation in northern Nagano Prefecture, central Honshu. These are identified with the following six species : Chlamys (Chlamys) cosibensis (Yokoyama), C. (C.) ingeniosa tanakai Akiyama, C. (C.) foeda (Yokoyama), C. (C.) insolita (Yokoyama), C. ("C.") lioica shigaramiensis Amano et Karasawa and C. (Leochlamys) tanassevitschi (Khomenko). The last species has hitherto also been known as Chlamys daishakaensis Masuda et Sawada or C. iwakiana (Yokoyama). The diversity of this chlamid fauna is attributed to the distributional pattern and geologic ranges of the species. Chlamys lioica shigaramiensis and C. tanassevitschi are confined to the northwest flank of the Orihashi Syncline, which was deeper and colder than the southeast flank area where C. foeda occurred. Chlamys ingeniosa tanakai, C. insolita and C. lioica shigaramiensis are Miocene relict forms. They survived in the studied area to the Middle Pliocene, owing to the cold-water embayment conditions. The mixture of Miocene and Pliocene type species accounts for the diversity of Chlamys from the Ogikubo Formation.
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  • KEI MORI
    1994 Volume 1994 Issue 176 Pages 677-678
    Published: December 30, 1994
    Released on J-STAGE: May 25, 2010
    JOURNAL FREE ACCESS
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