Abstract:  Described in this paper is a new amiine, ？Cyclurus orientalis, collected from the early to middle Eocene Xiawanpu Formation of Xiawanpu, Xiangxiang City, Hunan Province, China. It is unquestionably an amiine because of the diplospondylous vertebrae of both the normal and alternating types in its preural caudal region, the one-to-one fusion between the ural centra, except the first one, and the hypurals, the absence of the urodermals in the caudal skeleton, and the long dorsal fin. It is referred to ？Cyclurus because its first coronoid carries teeth with rounded tops. It is different from other species of ？Cyclurus in having fewer dorsal fin rays, deeper and shorter body, and fewer vertebrae and centra. During the Eocene when the transpacific distribution pattern reached its maximum, amiines were not uniquely shared by both sides of the Pacific and thus cannot be taken as an indicator of the transpacific distribution. Their wider, northern hemisphere distribution, along with the similar distribution of some other fish groups such as Esocidae and Osteoglossidae, may call for an alternative explanation by other special geological backgrounds.

摘要： 记述了弓鳍鱼亚科一新种：？Cyclurus orientalis (东方圆尾鱼)，标本采集于中国湖南省湘乡市下湾铺早始新世至中始新世下湾铺组。化石因具有以下特征而被归入弓鳍鱼亚科(Amiinae)：尾前椎为双椎型；除第一尾椎和第一尾下骨外，其余尾椎和尾下骨均一对一愈合；无膜质尾骨；背鳍长。因其第一冠状骨上的牙齿顶端圆钝，而被归入？Cyclurus属。本新种与？Cyclurus属中其他种的区别在于：背鳍鳍条较少；身体短而高；脊椎和椎体较少。在始新世淡水鱼类的跨太平洋分布达到鼎盛时，由于弓鳍鱼亚科并非仅分布于太平洋两岸的类群，因此不能作为跨太平洋分布的指示类群。弓鳍鱼亚科在北半球的分布范围更广，与某些其他淡水鱼类群例如狗鱼科(Esocidae)和骨舌鱼科(Osteoglossidae)相似，这种现象只能用有别于形成跨太平洋分布的地质背景来解释。