Paleozoogeographical study of Cenozoic molluscan fauna in Japan

1.分析了中中新世热带软体动物组合的分布。组合由红树林沼泽成分和其它成分组成。分布范围由南至新潟-山形地区，以八尾、富山和冈山-广岛的美北为代表。西表组与中中新世富山组的温度条件相似.在日本西南部，有两个动物群，下部的Akeyo动物群和上部的Kurosedani动物群，在中新世早期至中期被确认。两个动物群的年龄分别为18 ~ 16 Ma和16 ~ 15 Ma。黑尾目是典型的热带软体动物种。Akeyo由亚热带成分组成，而Kurosedani缺乏热带物种。中中新世时期，该地区古动物地理可划分为热带、亚热带和温带.研究了卡克川组和小笠组的软体动物区系。从西北部的亚浅海动物群到西南部的半深海动物群有明显的变化。种和组合的时间变化表现为伊藤川（1988）的I、II和III级变化.对伊藤川（1988）提出的软体动物区系时空分布等级的观点进行了验证。对不同地点渐新世和中新世的软体动物群进行了比较，并明确了其等级。

1. Distribution of tropical molluscan assemblages in Middle Miocene is analyzed. The assemblages consist of mangrove swamp elements and others. They distribute from south to Niigata-Yamagata area and are typical in Yatsuo, Toyama and Bihoku, Okayama-Hiroshima. Similar temperature condition is seen beween present Iriomote and Middle Miocene Toyama.2. In Southwest Japan, two faunas, the lower, the Akeyo and the upper, the Kurosedani faunas, are recognized in the early to middle miocene. The ages of the two faunas ale 18 to 16 Ma and 16 to 15 Ma, respectively. The Kurosedani includes typical tropical element spement species of molluscs. The Akeyo which consists of subtropical elements differs from the Kurosedani lacking Tropical species. tropical, subtropical and temperate paleozoogeographical divisions are recognized in Middle Miocene of the Jananese Islands.3. Molluscan faunas of the Kakegawa and Ogasa groups are studied. Remarkable change from the sublittoral fauna in northwest to the bathyal one in southwest is recognized. Temporal change of species and assemblages indicates Grade I, II and III changes of Itoigawa(1988).4. The idea of grade in molluscan fauna distribution in time and space shown by Itoigawa(1988) is checked. Molluscan faunas of Oligocene and Miocane in various localities are compared and the grade is clearly recognized.