Apparatus structure of the Ordovician conodont Decoriconus peselephantis (Lindström 1955)

The Lower Ordovician conodont species first described as Scolopodus? peselephantis Lindström 1955, has a seximembrate apparatus of laterally compressed, variously curved and flexed coniform elements. These are very small and invariably striated or multicostate. The taxon is reassigned to Decoriconus Cooper 1975, a genus hitherto known by species from Upper Ordovician and Silurian strata. These younger species share several characteristic morphological features with the older species investigated in this work. When studied in detail, it was discovered that D. peselephantis was the first species in a lineage which also included two successive new species. Of these, D. mercurius n. sp. occurs in the middle Arenig, while D. pesequus n. sp. ranges from the late middle Arenig and at least through the Llanvirn, possibly even into the Caradoc. These new species, which were previously included into S. ? peselephantis, are described and their geographic distribution investigated. In addition, a probable homeomorphic form of D. peselephantis, Toxotodus? gabriellae n. sp., is diagnosed.