Apically pointed, conical layers of calcareous material that may fill the siphuncle in some groups of nautiloids (Nautiloidea). The layers build forward from the rear of the conch.
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。