Revision of Some Lower to Middle Ordovician Leiostegiid and Associated Trilobites from Iran and China

A low-diversity Middle Ordovician leiostegiid trilobite association from Iran dominated by Pseudocalymene also includes Liomegalaspides and Illaenus sinensis, demonstrating strong biogeographical links with contemporaneous trilobite faunas from South China. The Iranian assemblage also includes a new species, Nileus jafari. The Iranian Pseudocalymene Association is comparable to the Asaphid-Pseudocalymene Association characteristic of the inner shelf of South China, but is less taxonomically diverse which may reflect its location at higher latitude. The affinity of Pseudocalymene with some Lower to Middle Ordovician leiostegiid genera from South China is discussed in detail.