皖北志留纪盔甲鱼类的新发现

GERASPIDIDAE, A NEW FAMILY OF POLYBRANCHIASPIDIDA (AGNATHA) FROM SILURIAN OF NORTHERN ANHUI

本文记述了盔甲鱼类的一新属种——珍奇秀甲鱼(Geraspis rara gen. et sp. nov.),它代表—新科(Geraspididae fam. nov)。头甲及其后覆盖鳞片部分呈正常连接。主要特征为:间带短,角呈狭长的三角形,伸向后方。侧背沟靠近头甲中背线。鳞为小而密集的菱形。

The Wenlockian agnathan specimen described in this paper was collected by a filed team of Anhui Regional Geological Bureau during the 1985 field season from the lowermost part of Maoshan Formation or the upper most part of Fentou Formation in Wuwei district, N. Anhui. Polybranchiaspidida Geraspididae faro. nov. Geraspis rara gen. et sp. nov. Diagnosis A polybranchiaspididan of medium size. Orbital opening small and situated near the middle line of cephalic shield. Median dorsal opening oval-like in shape, its length slightly shorter than breadth and situated near the rostral margin of cephalic shield. Cornua much longer and broader. The median part of cephalic shield between the cornua very short and with a deeply embayed posterion margin. Pectoral sinus not well developed. A pair of longitudinal dorsal lateral canals (Idc)situated near the middle line of shield, with four long transverse bra'nches (tr_(1-4)), infraorbital canal (ifc) short, median transverse canal (mtc) not developed, supraorbital canal (soc) V-shaped. Description This new genus is only based on a complete cephalic shield in dorsal view, behind the carapace, the posterior part of the body and the tail are covered with small scales. The following dimensions are estimated from the holotype (AF8508): Total length of body 110mm Maximum breadth of cephalic shield (include cornua) 44mm Maximum length of cephalic shield (include cornua) 41mm Length in the middle line of cephalic shield 27mm Length of cornu (tip to interzonal part) 17mm Discussion The median dorsal opening oval-like in shape, well-developed longitudinal dorsal lateral canals and supraorbital canals V-shaped require that this specimen be placed in the Polybranchiaspidida. This specimen is excluded from being that of Polybranchiaspis and Dayongaspis hunanensis by the position of dorsal lateral canals situated near the middle-line of the cephalic shield, and from Laxaspis and Dongfangaspis by the present of much longer and broader paired cornua, the median part of cephalic shield between the cornua (interzonal part) very short and with a deeply embayed posterior margin of shield in this new genus and species.