Cambrian series 3 agnostoid trilobites Ptychagnostus sinicus and Ptychagnostus atavus from the Machari Formation, Yeongwol Group, Taebaeksan Basin, Korea

This paper reports the successive occurrence of Ptychagnostus sinicus Lu, 1957 and Ptychagnostus atavus (Tullberg, 1880) from the lower part of the Machari Formation, Yeongwol Group, Korea. Morphometric approaches of using the landmark and principal component analyses make it possible to differentiate P. sinicus from P. atavus with clarity: pygidia of P. sinicus have a relatively narrow M1, a transverse F2, and a weakly developed M2 tubercle, whereas those of P. atavus are characterized by a broadly arching M1, a chevron-shaped F2, and a prominent M2 tubercle. Recognition of P. atavus, for the first time in Korea, allows the determination of the base of the Drumian Stage in Korea and aids correlation with other parts of the world.本论文报道了韩国宁越群（Yeongwol Group）马卡里组（Machari Formation）下部相继产出的中华毕彻球接子（Ptychagnostus sinicus Lu, 1957）与退化毕彻球接子（Ptychagnostus atavus (Tullberg, 1880)）。采用地标点分析（landmark analysis）与主成分分析（principal component analyses）的形态计量学方法，可清晰区分这两个物种：中华毕彻球接子的尾甲具有相对狭窄的M1结构、横向延伸的F2结构以及发育较弱的M2瘤突；而退化毕彻球接子的尾甲则以宽弧形M1结构、人字形F2结构以及显著突出的M2瘤突为典型特征。本次在韩国境内首次识别出退化毕彻球接子，据此可确定韩国德鲁曼阶（Drumian Stage）的底界，同时有助于与全球其他地区开展地层对比。