|AT LEFT:One of the "Ontario Eurypter- ids," Eurypterus dekayi is a common element of the Bertie Group Faunas. This form occurs only within the Wil- liamsville Formation but has a wide distribution. It is known from Byng in Ontario, Canada, eastward to Akron Falls where I collected a carapace at the base of the Williamsville Fm. It probably also occurs eastward to at least the Five Points area south of Rochester, New York where there is a reappearance of the characteristic Eurypterus lacustris Fauna with which this for is associated.
Note the wide carapace of this form and the (relatively) smaller eyes. The swimming legs are relatively large and the telson, not preserved on this specimen, is a sharp naillike spike.
E. dekayi evolved from Eurypterus laculatus, found abundantly in the Fiddlers Green Formation of Ontario, Canada and New York State.