- GeoRef, Copyright 2004, American Geological Institute. Reference includes data from Bibliography and Index of Geology Exclusive of North America, Geological Society of America, Boulder, CO, United States
Pristiograptus ludensis occurs in uppermost Wenlock shales and the Wenlock limestone of the Ludlow area (England). The P. ludensis (formerly P. vulgaris) zone is therefore considered to belong largely if not entirely to the Wenlockian. It is suggested that the base of the P. nilssoni zone be considered the Wenlock-Ludlow boundary, rather than the base of the P. ludensis zone.