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三叶虫掘头虫科古掘头虫属Protoryctocephalus Chow(Zhou)in Lu et al.,1974b由周志毅根据贵州丹寨南皋寒武系乌训组的标本命名,至今共有4个种:Protoryctocephalus wuxunensis,P.balangensis,P.elongatus,P.arcticus。贵州剑河八郎“清虚洞组”产其中的2个种:P.elongatus及P.arcticus。P.elongatus首现于“清虚洞组”上部,上延至凯里组下部;P.arcticus命名于格陵兰北部Peary Land的Henson Gletscher组中部,位于寒武系第5阶首现分子Oryctocephalus indicus层位之下,为格陵兰北部Peary Land的Henson Gletscher组与凯里组下部及“清虚洞组”上部的地层对比提供了化石依据,有助于寒武系第5阶地层对比。八郎“清虚洞组”P.elongatus及P.arcticus的发现具有演化及国际地层对比意义。
Trilobite exocarpus Protoryctocephalus Chow (Zhou) in Lu et al., 1974b by Zhou Zhiyi according to Guizhou Danzig Nangao Cambrian Osamu group specimen named, so far there are 4 species: Protoryctocephalus wuxunensis, P. balangensis, P.elongatus, P.arcticus. Guizhou Jianhe Hachiro “Qingxudongdong group ” producing two kinds of them: P.elongatus and P.arcticus. The P.elongatus first appeared on the upper part of the “Qingxudong Formation” and was extended to the lower part of the Carey Formation. P.arcticus was named in the middle of the Henson Gletscher Formation in Peary Land, northern Greenland, and was located in the fifth order member of the Cambrian Oryctocephalus indicus The horizons provide a fossil basis for the Henson Gletscher Formation of Peary Land in the northern part of Greenland in comparison with the lower part of the Carey Formation and the strata above the “Qingxuendong Formation”, which contributes to the Cambrian fifth-order stratigraphic correlation. The discovery of P.elongatus and P.arcticus in Hachiro and Qingxudong Formation has the significance of evolution and international stratum correlation.