"P. marylandicus", from deposits of Ludfordian (Late Silurian) age, is known from a fragmentary and small telson from the McKenzie Formation, Maryland first described by Kjellesvig-Waering in 1964, who recognized it as a telson of a "Pterygotus". The specimen (No. 140901 at the United States National Museum) is very wide, 0.75 cm, and has a nearly straight base with the margins converging anteriorly. Unlike some species, there are no serrations on the telson and the spine is blunt. The species is very distinct, being distinguishable from all other Silurian species of "Pterygotus" by the shape of its telson. A species of "Jaekelopterus", "J. howelli" from the Early Devonian, is similar in the wide and truncated telson shape, but is easily distinguished by possessing serrations and a much larger terminal spine.