PTYCHOPARIID TRILOBITES OF THE LOWER-MIDDLE CAMBRIAN BOUNDARY INTERVAL, PIOCHE SHALE, SOUTHEASTERN NEVADA

Twelve ptychopariid species assigned to five genera occur in the Lower-Middle Cambrian boundary interval, Pioche Shale, eastern Nevada. New taxa include one genus, Eokochaspis, and seven species, Eokochaspis nodosa, E. delamarensis, E. metalaspis, E. longspina, Kochina? walcotti, Mexicella antelopea, and M. robusta. Two new biozones, the Eokochaspis nodosa and overlying Amecephalus arrojosensis Biozones, are proposed between the Lower Cambrian Olenellus Biozone and the Middle Cambrian Plagiura-Poliella Biozone. In addition, the three remaining informal shale members of the Pioche Shale are formally named.