A REVIEW OF ORDOVICIAN AGNOSTID GENERA (TRILOBITA)

The definition and scope of Ordovician genera of agnostid trilobites a re discussed, and the generic affiliation of Ordovician species and we ll-illustrated material referred to in open nomenclature is assessed. Some 198 Ordovician species plus 25 species of uncertain latest Cambri an/earliest Ordovician age are enumerated, representing 24 genera and subgenera, of which Geragnostus (Novoagnostus) n.subg. and Lotagnostus (Semagnostus) n.subg. are new. Geragnostella is ranked as a subgenus of Geragnostus. The species of Arthrorhnchis are tentatively divided a mong a tardus species group and an elspethi species group. Species of Dividuagnostus are divided among a sensu stricto group and an early sp ecies group. Pseudorhaptagnostus Lermontova, 1951 is restored as senio r synonym of Neoagnostus Kobayashi, 1955. It is concluded that Ordovic ian agnostids were largely adapted to temperate and colder water habit ats.