论寒武纪三叶虫节头虫属:概念和异名

Restudy on the Genus Arthricocephalus( Cambrian) : concept and synonyms

节头虫属(Genus Arthricocephalus)的概念一直较为混乱,在为它的模式种乔氏节头虫(Arthricocephalus chauveaui)指定"选模"后,又进一步加剧。经对A.chauveaui的原始手标本上保存的所有三叶虫研究后,发现命名者Bergeron所附A.chauveaui的唯一图片,依据的是其中一枚背壳,特征吻合,从而认定该背壳是A.chauveaui的正模,代表了模式种和节头虫属的概念,是该种和该属名称的载体。也表明为A.chauveaui建立"选模",既无必要,也违背命名者的本意。而且选择一个不归属于A.chauveaui的标本来代表该种、该属的概念,就更不妥当。经研究,手标本上的三叶虫不是同一个种,而是隶属于三个不同种,这三个种又应归属于三个不同的属,即Arthricocephalus,Oryctocarella和Duyunaspis。A.chauveaui"选模"头盖并不属于该种,应归属于Oryctocarella duyunensis。研究还表明,有三个分类单元是Arthricocephalus的晚出异名,即Arthricocephalus(Arthricocephalites)Chien et Lin in Lu et al.,1974,Haliplanktes Blaker et Peel,1997,和Arthricocephalites Chien et Lin sensu Yuan et al.,2002。

The generic concept of Arthricocephalus is a matter of great confusion,and the confusion has been exacerbated by establishment of so- called lectotype for its monotypic type species Arthricocephalus chauveaui Bergeron,1899（ Lane et al.,1988）. In fact,a diagram of the exoskeleton illustrated by Bergeron for the type species was apparently based on a single exoskeleton that is easily identifiable among the specimens used to establish the type species,obviating the necessity for designation of a lectotype. This exoskeleton should be regarded as holotype of the type species that bears the generic concept of Arthricocephalus as revised. The slab that Bergeron studied contains four exoskeletons,one cranidium and one pygidium,all of which,as revised,do not belong to a single species but to species assigned to three separate genera,Arthricocephalus,Oryctocarella and Duyunaspis. The so-called lectotype selected by Lane et al.（ 1988） for the type species of Arthricocephalus does not belong to Arthricocephalus chauveaui but to Oryctocarella. A specimen different greatly from the original illustration is selected as lectotype against author＇s original intention. Three taxa are regarded as junior synonyms of Arthricocephalus,i. e. Arthricocephalus（ Arthricocephalites） Chien et Lin in Lu et al.,1974,Haliplanktes Blaker et Peel,1997,and Arthricocephalites Chien et Lin sensu Yuan et al.,2002.