Pseudocalymene superba Pillet Dapingian to lower Darriwilian, Shirgesht Formation, Unit B3, Derenjal Mountains, eastern central Iran. The trilobites in the present study were sampled from the upper part of the Shirgesht Formation, which is best exposed on the west side of the Dahaneh Kolut Valley (Fig. Our observations suggest that there is no continuous sequence through the Lower to Middle Ordovician rocks in the area and that all published sections are composite. 2004) revised the succession of the Shirgesht Formation and provided some information on fossil localities. A detailed description of the geology of the area was provided by Ruttner et al. Here the uppermost Cambrian to Middle Ordovician Shirgesht Formation is exposed on both sides of the Dahaneh Kolut Valley. GEOLOGICAL SETTING Iran The type locality of Pseudocalymene superba and Paraonychopyge iranica Pillet, 1973 is situated in the southern part of the Derenjal Mountains, about 10 km northwest of Shirgesht settlement, and 65 km north of the city of Tabas (Fig.

New collections of trilobites from the Lower to Middle Ordovician Shirgesht Formation of Iran and from the Lower to Middle Ordovician of South China provide us the opportunity to complete a comparative study of Iranian and Chinese leiostegiid genera and to resolve some taxonomic problems raised in previous publications. In that paper, Pseudocalymene was considered in a very wide sense as a senior synonym of Paraonychopyge Pillet, 1973 Eucalymene Lu, 1975 Paraszechuanella Liu in Zhou et al., 1977 and Madaoyuites Liu in Zhou et al., 1977. (2004), who gave a detailed description of the type species Pseudocalymene superba Pillet, 1973. Iranian trilobites from the Shirgesht Formation have recently undergone substantial revision by Bruton et al. Following a brief note by Pillet (1976) on the possible synonymy of Pseudocalymene and Eucalymene, this view was accepted by Fortey & Shergold (1984) and Zhou et al. Attribution of Pseudocalymene and Eucalymene to the Leiostegiidae has been widely accepted since Fortey & Shergold (1984) demonstrated that the family Eucalymenidae Lu, 1975 must be considered as a junior synonym of the Leiostegiidae Bradley, 1925. A P a r a o n y c h o p y g e a n d Pseudocalymene were originally described from the Lower to Middle Ordovician Shirgesht Formation of central Iran by Pillet (1973), and a third genus, Eucalymene, was reported by Lu (1975) from strata of almost the same age in South China.

A.t.o.m. arriw