"P. problematicus" was also used as the designation for an incomplete chelicera discovered in the Welsh Borderland of western England by John William Salter in 1852 but is in modern times considered a "nomen vanum" ("baseless name") as the species is impossible to define. The fossil material with which it was described is undiagnostic and insufficient to establish any meaningful characteristics and as such many fragmentary pterygotid fossils have been referred to it throughout its long history, rendering it effectively synonymous with the family Pterygotidae. More often than not, these fragments consist of patches of pterygotid integument preserving the scale-like ornamentation characteristic of the group which researchers have wrongfully believed was characteristic of only "Pterygotus" or "P. problematicus". As such ornamentation is known from every pterygotid genus it can not be used as a diagnostic feature of a single species. Though "P. problematicus" is the earliest name used for a species of "Pterygotus", it is not considered the type species as the name is no longer in use. Instead "P. anglicus", based on a number of diagnostic features and properly illustrated in its description by Agassiz in 1844, is considered the type species of "Pterygotus".