even more elongated than in Slimonia and ended in a tri-lobed structure unique to the genus. Though Slimonia itself is very well known, the other genus of the family, Salteropterus, is less well known with its fossils only preserving the telson and the metastoma (a large plate part of the abdomen). As such it is difficult to establish exactly which traits distinguish the family as a whole from the other pterygotioid eurypterid families (Pterygotidae and Hughmilleriidae), even though several defining traits are known of Slimonia. Many of the unique traits of Slimonia are found in the carapace (the "head"), which is not known in Salteropterus. Among these is the quadrate (square) shape of the carapace itself and the placement of the compound eyes on the frontal corners. Though they were closely related, the Slimonidae had small and non-developed chelicerae (frontal appendages) in comparison to the Pterygotidae, which possessed well-developed and powerful cheliceral claws. History of research The type species of Slimonia, S. acuminata, was first described as a species of Pterygotus, "Pterygotus acuminata", by John William Salter in 1856 based on fossils that had been discovered in Lesmahagow, Scotland. That same year David Page erected a new genus to contain the species, as several distinctive characteristics made the species considerably different from other known species of Pterygotus, among them the shape of the carapace and P. acuminata lacking the large cheliceral claws otherwise characteristic of Pterygotus. The genus was named "Slimonia" after Robert Slimon, honoring the Welsh fossil collector and surgeon who was the first to discover eurypterid fossils in Lesmahagow. In the late 1800s and early 1900s new specimens were discovered of a previously fragmentary species of Eurypterus, E. abbreviatus, in Herefordshire, England. One of these specimens, BGS GSM Zf-2864 (discovered in 1939), revealed a very distinct telson and features similar to Slimonia (such as the last three opisthosomal segments tapering in a way similar to in Slimonia), which suggested a close relation between this species and Slimonia. The family Slimonidae was erected as a taxon by Nestor Ivanovich Novojilov in 1962 to contain the genus Slimonia, which was considered sufficiently distinct from the genera housed in its previous family, the Hughmilleriidae. After several features had been noted that suggested a close relationship between Salteropterus and Slimonia (particularly similarities in the abdominal segments), Salteropterus was finally classified as a slimonid in 1989 by Victor P. Tollerton. Paleobiology The large