宽背虫属Bathynotus (Hall, 1859)广泛分布于劳伦古大陆、中国华南地区、澳大利亚和西伯利亚, 为寒武纪第二世末期最重要的标志性三叶虫之一,已成为寒武系划分的重要指示化石。其模式种B. holopygus以其狭长的颊刺、胸轴宽, 第11节肋刺巨大, 第12、13节肋刺不发育为主要特征;具有很强的地域性, 仅分布于华南和北美, 在华南主要见于寒武系扬子区与江南区之间过渡区的黔东地区。B. holopygus产出地层延限较窄, 仅见于寒武系第二统第四阶顶部。本文所描述的部分标本采自贵州剑河八郎苗板坡剖面苗岭统及乌溜阶界线之下2 m左右, 是在该地的首次报道, 也是全球仅有的第4个产地。笔者通过数理统计值分析进一步描述B. holopygus的特征和发育趋势, 为进一步属种研究提供新材料; 根据新发现的唇瓣标本进一步推测其唇瓣与腹边缘为愈合状态。

Bathynotus (Hall, 1859), occurs widely in Laurentia, South China, Australia and Siberia. Bathynotus holopygus (Hall, 1859), one of the representative trilobites of late Cambrian Series 2, has been a dramatic index fossil for the subdivision of the Cam-brian System. The type species of this genus is characterized by its long and slender genal spine, wide axis and a well-developed macropleural spine on 11th segment followed by two distinctly narrow segments; with a narrow geological range and only occurs in South China and North America. The material from South China is mainly found in East Guizhou of the transition zone between the Yangtze Platform and Jiangnan Basin. The vertical extension of B. holopygus-bearing stra-ta is short and only restricted at the top of the Cambrian Stage 4. The appearance of B. holopygus provides an important global stratigraphic marker of the boundary between Cambrian Series 2 and Miaolingian Series. The specimens described in this paper were collected from the layer that is 2 m below the boundary of Wuliuan Stage of Miaolingian Series. This dis-covery is not only the first documentation of this species in the area but also the fourth locality recorded for this species glob-ally. This study deeply describes the characteristics and developmental trends of B. holopygus through the mathematical anal-ysis of its parameters, and provides new materials for the study of this genus. According to the newly discovered specimens, it is inferred that the rostral plate is fused with the hypostome.