"eysyslopterus" is only known from one single specimen (and is therefore the holotype, amnh 32720, housed at the american museum of natural history) which preserves the carapace. this fossil was collected by the american biologist and zoologist william patten during his extensive explorations at the rootsikula formation in saaremaa, estonia (then part of the soviet union). during a meeting between patten and the norwegian paleontologist and geologist leif størmer in 1932, størmer observed patten's private collection of eurypterids, among which he recognized a carapace of a new unknown species. he described it in 1934 as belonging to the genus "hughmilleria patteni", named after patten, who died months after the meeting. størmer noticed several differences between his new species and other "hughmilleria" species, essentially the shape of the prosoma and the form or position of the eyes. he also suggested a close relationship between "h. patteni" and other species, especially the scottish species "h. lanceolata".