sentences:  In 1899, an additional species, "S. dubia", would be referred to the genus.This species was recovered from slightly earlier deposits (Llandovery age) in the Pentland Hills of Scotland and could be distinguished from "S. acuminata" by the more elongated telson (also not as broad in the parts furthest back), thinner telson spike and a slightly different, tapering, body shape that tapers evenly the whole way instead of suddenly narrowing near the seventh segment as in "S. acuminata".The type specimen of "S. dubia" is a badly preserved carapace, with fragments of various degrees of completion of the first eleven segments found associated.