关键词: 刘家场, 奥陶系, 花瓣海百合

Abstract:

The materials treated in this paper were collected from the Lower Ordovician Dawan Formation of Liujiachang,Songzi County,Hubei Province by Dr.Liu Binli in 1991.Two specimens have been identified to be a new genus—Eopetalocrinus(gen.nov.)from the arm structure,and it is placed provisinally Family Petalocrinidae.This discovery is con-siderably important in studying the genesis and the evolution of Petalocrinidae.The arms differ from those genera's,which belong to petalocrinidae in lateral conjunction.All members of the Family Petalocrinidae were discovered from the Silurian,except for the new genus which exists in the Early Ordovician.Perhaps the present new genus is an an-cestry from the arm structure.The evolutional relationship among all genera of the Petalocrinidae may be shown as follows:Eopetalocrinus(gen.nov.)→Petalocrinus→Sinopetalocrinus→Spirocrinus.Description of new genusEopetalocrinus(gen.nov.)Description There are five arm-fans,which are connected with each other like a flower with five petals fully expanded.Outline is almost rhombic due to the regeneration of about 40 mm long and 26 mm wide,but it is a subcircular in the original shape.The arm-fan has an 75°angle with 18—28 grooves on the ventral surface except a smallarm-fan,which has an angle only about 50°with 6 grooves.The grooves are proved bythe mode of branching with Ⅱ-Ⅳ times.The dorsal surface is smooth.The articualr facets are about fusiform in shape,their insides formed a pentagon about 5 mm in diameter. Type species Eopetalocrinus sinensis(gen.et sp.nov.)Distribution and Age Early Ordovician,Hubei,China.