江西上三叠统安源组叶肢介一新属*

香溪叶肢介亚科(Xiangxiellinae)以壳瓣胎壳较大、壳上具有一条或两条短脊为特征,包括两个属:原单脊叶肢介属(ProtomonocarinaTasch,1962)和香溪叶肢介属(XiangxiellaShen,1976)。该亚科化石广布于世界各地,最早出现于我国晚石炭世,三叠纪末消失。本文建立的新属叉脊叶肢介(Dicerestheriagen.nov.),以胎壳上具有两条呈“人”字形向前后分叉的、粗壮的短脊为特征,与香溪叶肢介的构造特征最为接近。推测新属壳瓣胎壳脊的形成与闭壳肌附着引起的壳瓣变异或与生态环境变化有关。化石产于江西抚州崇礼县礼陂煤矿,上三叠统安源组徐坊段。湘赣一带安源组为一套含煤地层,属于滨海、近海、沼泽沉积区,产半咸水类型的双壳类,时代认为卡尼及早诺利期。植物化石Ptiozamites–Anthrophyopsis组合是诺利期的代表,适宜于热带、亚热带气候,滨海环境生长的群落。因此推测新属是一个生活在炎热、潮湿的热带-亚热带气候近海沼泽环境的类型。

A new genus of clam shrimp from the Upper Triassic Anyuan Formation of Jiangxi, China

The clam shrimp Xiangxiellinae (Spinicaudata), characterized by one or two short ribs on the large larval valve, is comprised of two genera: Xiangxiella Shen, 1976 and Protomonocarina Tasch, 1962. The members of this subfamily are widely distributed in the Upper Carboniferous to the Triassic strata in the world. The new genus Dicerestheria gen. nov. is established based upon specimens from the Upper Triassic Xufang Member of the Anyuan Formation in Wuzhou City, Jiangxi Province. Its large larval valve bears two bifurcate, short, and stout ribs. It is very similar to Xiangxiella in that they both have two ribs on the larval valve, but the ribs of the new genus are much stronger than those of the latter. The growth bands of the new genus are ornamented with medium reticulate sculpture. It is speculated that the larval valve ribs might be caused by variation of attachments of the adductor muscles, or by changes of their habitat and living environments. The Anyuan Formation consists of a set of coal-measure sediments, yielding brackish bivalves and abundant Norian plants represented by the Ptiozamites-Anthrophyopsis flora, reflecting an environment in humid tropical-subtropical climate. Therefore, the new genus may have lived adjacent to nearshore marsh environments in warm and humid tropical-subtropical climate.