A new genus and species of synziphosurine (Chelicerata) is described from the Silurian (Wenlock) Scotch Grove Formation Konservat-Lagerstätte in Clinton County, Iowa. Camanchia grovensis n. gen. n. sp. is characterized by a sub-triangular carapace, ten opisthosomal segments divided into a preabdomen of seven and a postabdomen of three, and a tuberculate ornament on the carapace and pleural margins. A single new specimen from the same location is assigned to Venustulus waukeshaensis, originally described from the Late Llandovery Waukesha Konservat-Lagerstätte of Wisconsin. A comparison of the musculature of C. grovensis with that of living Limulus polyphemus and the Jurassic Mesolimulus walchi from Nusplingen, Germany shows that it is much simpler, consistent with the status of synziphosurines as stem xiphosurids.