Abstract Ordovician trilobites are reviewed based on a new species-level relational database. The stratigraphical ranges of all 56 families with occurrences in the Ordovician are documented and the content, phylogenetic status, diversity and Ordovician distribution by major palaeocontinent/terrane are discussed. Aspects of higher classification are also dealt with. Global sampling is heavily biased towards a small number of highly sampled areas. Much of the world has a very limited record of formally named trilobite species. Even within heavily sampled units, sampling is patchy by environment and time. Genus endemism was at a peak in Laurentia, Baltic, and Avalonia in the Floian and declined more-or-less steadily through the remainder of the Ordovician.

Abstract The early Late Ordovician (Sandbian 1) representatives of the Tafilalt Biota in the locality of Bou Nemrou (Jbel Tjarfaïouine) provide examples of fossil preservation in medium-grained sandstones with abundant microbially induced sedimentary structures. The recorded trilobite assemblage comprises 11 species of ten genera, among which one is new ( Placoparia africana Pereira & Gutiérrez-Marco, sp. nov.) and four others previously regarded as endemic to the locality are considered to be synonymys of species already described from Bohemia. The oldest representative of the illaenid genus Cekovia is recorded, revised diagnosis proposed for the genus Mytocephala Struve and for Uralichas tardus Vela & Corbacho. Parvilichas Corbacho & Vela is considered to be a junior synonym of Uralichas Delgado. From a palaeobiogeographical point of view, the Bou Nemrou locality shows strong relationships with trilobite assemblages from the Dobrotivian and with the lower Berounian sandstone facies of Bohemia, reinforcing the correlation of both regions. Some soft-bodied structures are recognized here, including the digestive tracts of Uralichas and the traces of paired, metameric axial bands in the anterior thoracic segments of the trilobite Selenopeltis preserved in apatite and interpreted as intersegmental musculature.