In 1964, two species described by Kjellesvig-Waering increased the known range of "Pterygotus" to Scotland ("P. lanarkensis") and Estonia ("P. impacatus"), both Ludlow in age. "P. lanarkensis" was the second pterygotid to be discovered from the well known eurypterid fauna of Lesmahagow in Lanarkshire, Scotland. As pterygotids commonly occur in association with multiple related genera, it was considered unusual that there was only one species, "Erettopterus bilobus", present in Lesmahagow. Fossil remains of "P. lanarkensis" had been known since 1868 (first collected by Robert Slimon in 1855-1860), but were first recognized as such by Kjellesvig-Waering in 1964. Represented by a large chelicera (specimen number 53890 in the British Museum of Natural History) originally doubtfully referred to "Erettopterus bilobus", "P. lanarkensis" more closely resembles "P. anglicus" than it does species of "Erettopterus". The terminal tooth (broken in this specimen) is 0.9 cm in length and the central tooth is unusually short. The combination of an unusually long terminal tooth and an underdeveloped central tooth differentiates "P. lanarkensis" from other species of "Pterygotus". Several features distinguish it from the "Erettopterus" that it was found associated with, including the more robust chelicerae of "P. lanarkensis".