Oktavites spiralis（Geinitz，1842）是志留系特列奇阶（Telychian）的笔石带化石，其形态特征明显，在全球范围内广泛分布，地层对比意义较强。然而，该种宽泛的化石定义以及缺乏居群差异研究，造成了对该化石延限的争议，不利于地层的精确对比。笔者对产自陕西紫阳、岚皋地区特列奇阶Oktavites spiralis带至Cyrtograptus lapworthi笔石带的45个Oktavites spiralis不同发育阶段的幼体标本进行研究，建立了较完整的发育序列，从而对该种的始部特征有了更为深入的了解，增加了描述的精确性。同时，通过始部特征的对比研究，可将Oktavites spiralis和与之共生的Oktavites contortus (Perner，1897）明确区分为2个独立的种。此外，对Oktavites spiralis和Oktavites contortus发育过程的研究，也可成为该属进一步精确厘定的主要依据之一。

A graptolite index species of Telychian Age (late Llandovery, Silurian), Oktavites spiralis Geinitz, 1842, is significant in stratigraphy correlation due to its typical morphological characters, rapid evolution and global distribution. However, controversies on the stratigraphic range of the species derived from the its broad definition without information of population variation has led to difficulties in regional correlations. In order to increase the accuracy of description, 45 specimens of Oktavites spiralis with different developmental stages have been collected from Oktavites spiralis Zone to Cyrtograptus lapworthi Zone (Telychian stage) in the Ziyang–Langao area, and its developmental sequence has been established according to the larvas which the sicula and proximal rhabdosomes are also well preserved. Meanwhile, the Oktavites spiralis and coexiting species Oktavites contortus can be further distinguished according the different morphology of the proximal rhabdosomes, which is also a key to define this genus precisely.

国家自然科学基金青年基金项目（41302006），中国地质调查局项目（1212011120144，12120114078101，121201011000150006）和中国地层委员会项目（1212011120142）联合资助。