An order of Trilobita that lived from the Middle Cambrian to Middle Devonian. They were medium-sized to very large, usually spiny, and in many the pygidium is larger than the cephalon. There were three suborders.
科学参考收录了60776条科技类词条，基本涵盖了常见科技类参考文献及英语词汇的翻译，是科学学习和研究的有利工具。