Article: A revision of some Ordovician graptolites of eastern North America

In a study of part of Hall's type material, lectotypes are proposed for Climacograptus bicornis (Hall) and Climacograptus spiniferus Ruedemann. The variation in the proximal end of the latter is amply illustrated and discussed; it is also suggested that the latter may betIhe slightly modified descendant of the former. Climacograptus parvus Hall ( C. phyllophorus Gurley) is considered to be conspecific with Pseudoclimacograptus scharenbergi (Lapworth) and Orthograptus amplexicaulis (Hall) is revised and the question of its priority over Orthograptus truncatus (Lapworth) is considered.In a review of part of Ruedemann's type material, the types of Climacograptus eximius Ruedemann are interpreted as consisting of deformed specimens of Pseudoclimacograptus modestus (Ruedemann) and of Climacograptus brevis strictus (Ruedemann); Climacograptus tenuis Ruedemann is considered to be conspecific with Climacograplus pygmaeus Ruedemann: Climacograptus Iorrainensis Ruedemann is assigned to Glyptograptus, and the name Climacograptus putillus (Hall) is temporarily restricted to the types in the American Museum of Natural History. Corynoides calicularis var. americana Ruedemann is revived and raised to specific rank as Corynoides americanus; the types of Corynoides comma Ruedemann are interpreted as deformed individuals of Corynoides americanus or C. calicularis sensu lato.The systematic treatment is preceded by a review of Ihe Middle-Upper Ordovician zonation hitherto recognised in the graptolite succession of eastern North America which is strongly provincial, containing faunas unknown outside this pan of the continent. The zonation is extended downward with the addition of the Diplograptus multidens and Nemagraptus gracilis Zones and expanded with data gathered since it was first proposed (Riva 1969).