Kennedy, W. J. (William James)Cobban, William A., 1916-2015.Landman, Neil H.2005-10-062005-10-061999http://hdl.handle.net/2246/30508 p. : ill. ; 26 cm.Includes bibliographical references (p. 7-8).The middle Campanian (Upper Cretaceous) zone of Baculites gregoryensis Cobban, 1951 in south-central South Dakota and eastern Wyoming has yielded numerous fragments of a distinctive species of Didymoceras characterized by initial loose planispiral whorls followed by loose helical whorls, and finally by a slightly pendant body chamber. These fragments are referred to Didymoceras cochleatum (Meek and Hayden, 1858), a species based on one-half of a septate whorl from the helical growth stage. This species is abundant in the Gregory Member of the Pierre Shale along the Missouri River Valley in South Dakota, rare in the Red Bird Silty Member of the Pierre Shale in eastern Wyoming, and very rare in the Rock River Formation in southeastern Wyoming.2561677 bytesapplication/pdfen-USQL1 .A436 no.3268 1999Didymoceras cochleatum.Ammonoidea -- South Dakota.Ammonoidea -- Wyoming -- Niobrara County.Mollusks, Fossil -- South Dakota.Mollusks, Fossil -- Wyoming -- Niobrara County.Paleontology -- Cretaceous -- South Dakota.Paleontology -- Cretaceous -- Wyoming -- Niobrara County.Paleontology -- South Dakota.Paleontology -- Wyoming -- Niobrara County.Pierre Shale.text