Eurypterus cyclophthalmus Laurie, 1892 from the Llandovery of the Pentland Hills, Scotland, is redescribed and assigned to the stylonurid eurypterid genus Kiaeropterus Waterston. 1979, previously only known from Kiaeropterus ruedemanni (Størmer, 1934) from the Wenlock of Norway. Another species previously assigned to Kiaeropterus, K. otisius Clarke 1907, is reassigned to the previously monotypic genus Clarkeipterus Kjellesvig-Waering 1966. The genus Kiaeropterus shares a previously unrecognized synapomorphy with the genus Brachyopterus Størmer 1951, namely a large bulbous ‘ocellar area’. In Kiaeropterus this area is cardioid whereas it is triangular in Brachyopterus. The two genera also share a number of less significant characters such as large anteriorly converging crescentic eyes, a lack of cuticular ornament and podomeres of the prosomal appendages with pronounced ridges, supporting a phylogenetic relationship between Kiaeropterus and Brachyopterus.

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