高罗王冠虫(Coronocephalus gaoluoensis Wu,1979)的再研究

RESTUDY OF CORONOCEPHALUS GAOLUOENSIS WU,1979

标本采自湖南省永顺县万民乡志留系下部Llandovery统Telychian阶秀山组上部,几乎全部为Coronocephalus gaoluoensisWu,其中有20多块头、胸、尾相连的完整标本。研究发现,Coronocephalus gaoluoensis Wu具有十分特殊的头部构造,其面线前支横切头鞍前叶中前部,头鞍前叶前部由两个自由颊额叶和一个双头刺组成,头鞍前叶前侧角在自由颊上。双头刺即背-腹边缘板,位于头甲背面头鞍前部。背沟在头部前侧角与边缘沟弧形相连,无头鞍前沟。头鞍后部收缩、向前膨大并逐渐变平,3对头鞍沟位于头鞍后侧最窄处,其中后2对横越头鞍,前面1对不相连。头甲前部光滑,中后部有稀疏的小瘤,两侧有许多小陷坑,边缘分布有规则的三角形短刺。唇瓣五边形,中心体凸,鼻状凸起明显。胸甲长方形,宽大于长,胸节11节。第7胸肋为大肋节,外端膨大,向后伸出大肋刺。尾甲大,三角形,尾轴分节40节以上,尾肋由15—16个肋节组成。尾肋刺发育,尾腹边缘窄,位于尾肋刺之下,无尾边缘。Coronocephalus gaoluoensis的面线型式完全可以与Coronocephalus rex和"Senticucullus"对比,属于Encrinuridae科的特殊亚科。

Amongst new specimens collected from the upper part of the Telychian Xiushan Formation of Llandovery（Lower Silurian）,at Wanmin town in Yongshun County,western Hunan,nearly all are assigned to Coronocephalus gaoluoensis Wu.More than twenty are whole and articulated specimens,thus providing a sound basis for the study presented here.The cephalon of this trilobite is very peculiar.Its anterior sections of the facial sutures traverse across the glabella at the mid-anterior part of the frontal lobe.The anterior portion of the frontal glabellar lobe comprises two fore parts of librigenae and a dual frontal glabellar spine.The dual frontal glabellar spine,i.e.,the dorsal-rostral plate,is located in the front of the glabella on the dorsal shield.The axial furrows join the marginal furrow at the antero-lateral edge of the cephalon,lacking the preglabellar furrow.The glabellar is contracted at its posterior,but the anterior is expanded and flattened.In the posterior part of the glabella,there are three pairs of glabellar furrows,of which the two posterior pairs go across the glabellar and the anterior pair is discontinuous.The cephalon is smooth anteriorly,tuberculate proximally and pitted laterally,with regularly triangular short spines on the margin.The hypostoma is pentagonal in outline,with a convex median body and distinct rhynchos.The thorax is quadrate in outline,wider than long,and composed of 11 segments.The 7th segment is a macropleura which expands distally and ends in a posteriorly extending macropleural spine.The pygidium is comparatively large and triangular in outline,with more than 40 axial rings and about 15—16 pleural ribs.A narrow doublure lies under the fine posterior pleural spines,lacking a marginal border.The present Coronocephalus gaoluoensis,in terms of its pattern of facial suture,is almost identical with Coronocephalus rex and Senticucullus.They may all be assigned to a distinctive subfamily of Encrinuridae.