A single bed at the base of the Jordan Sandstone in a road cut at Arcadia, Wisconsin, yielded an undescribed Late Sunwaptan (Saukia Zone) trilobite fauna that includes at least four species from the families Dikelocephalidae Miller, 1889 and Eurekiidae Hupé, 1953. Arcadiaspis bispinata n. gen. and sp. is a distinctive eurekiid that is characterized by paired occipital and thoracic axial spines, long genal spines, and a nonspinose pygidial margin. Other genera present are the dikelocephalids, DikelocephalusOwen, 1852 and CalvinellaWalcott, 1914, and the eurekiid, EurekiaWalcott, 1916. Type material of Calvinella spiniger (Hall, 1863) is illustrated photographically for the first time. A new eurekiid species, Corbinia burkhalteri from the Fort Sill Formation, Oklahoma, is also described.

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