非海相双壳类江西蛤（Jiangxiella）首次发现于日本

首次报道日本西南部发现的晚三叠世非海相双壳类江西蛤（Jiangxiella)，并讨论这一发现的意义。认为原产于湘、赣、粤地区的江西蛤是地理分布极有限的土著属，它在日本西南部的发现表明当时该区与华南东部的古地理关系极为密切，可能原属同一地块。

Jiangxiella, an Upper Triassic Non-marine Bivalve,Found from Southwest Japan

This paper reports the occurrence of a non-marine Upper Triassic bivalve genus Jiangxiella found from the Inner Zone of Southwest Japan. Jiangxiella was previously known to be a brackish-water or oligohaline-water form in southeastern China. The discovery of the genus in Southwest Japan may be beneficial to understanding the palaeobiogeographic relationships between two regions.The present material is collected from the Nariwa Group in Okayama Prefecture of Southwest Japan. In the area the Nariwa Group is divided into four formations as follows (in descending order): Jito Formation: mainly sandstone, more than 1000 m thick, containing marine bivalves Monotis (Entomonotis) ochotica and its varieties; Hinahata Formation; sandstones and shales interbeded with coal, more than 500 m thick, yielding abundant plant fossils and non-marine bivalves Jiangxiella and Unionizes?; Mogamiyama Formation: composed of sandstone, conglomerate and shale with coal-beds, 400-750 m thick, containing plant fossils; Kyowa Formation: more than 95 m thick, consisting mainly of sandstones and shales with coal seams, yielding marine shells such as Minetrigonia, Oxytama and Palaeopharus. Japanese scientists draw a conclusion that the Minetrigonia-Oxytama-Palaeopharus fauna of the Kyowa Formation can be correlated with some other faunas of the Outer Zone of Japan, suggesting a Carnian age, while the Monotis (Entomonotis) ochotica fauna of the Jito Formation is dated as late Norian or Rhaetian. Therefore the authors believe that the Jiangxiella-bearing beds of the Hinahata Formation is presumably equivalant to early-middle Norian in age according to its occurrence in the stratigraphic sequece of the Nariwa Group. Jiangxiella has, however, a longer range in southeast China according to previous records, probably from lower Carnian to upper Norian (or Rhaetian). It is restricted to a relative small basin, probably a brackish-water bay, namely the Xian-Gan-Yue bay, located at Jiangxi, Hunan and northern Guangdong of southeast China. The genus occurs usually in association with some marine or brackish-water forms such as Isognomon, Waagenoperna and Bakevelloides, and some fresh-water forms (U-nionids). But it has never been traced in marine deposits or in fluvial and lacustrine deposits, therefore, it may be limited in a very narrow area. The authors consider that Jiangxiella did not migrate or was dispersed from China to Japan through sea-ways or palaeo-land ways, and that the Chinese and Japanese localities were probably originally very closed to each other in late Triassic time. The blocks theirin were seperated and moved by plate tectonic movements later.