The cephalopod fauna of the Rockford Limestone was restudied on the basis of a collection made from a locality about 4 mi N. of the type locality. All species identified have been reported previously from the type Rockford. Based on the Kinderhook-Osage boundary determined by Rexroad and Scott on the basis of conodont faunas, these cephalopods appear to be of earliest Osage age. In the northern Indiana Rockford locality reported by Gutschick and Treckman, the cephalopods appear to be entirely Kinderhook in age, therefore older than the Rockford of the type area. Protocanites lyoni and other Rockford cephalopods previously thought to be representative of the Kinderhook may therefore characterize lowermost Osage strata as well.

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