Landman, Neil H.; Tsujita, Cameron J.; Cobban, William Aubrey, 1916-; Larson, Neal L.; Tanabe, Kazushige.; Flemming, Roberta L.
(New York, NY : American Museum of Natural History, 2006)
"We describe upper and lower jaws of Placenticeras Meek, 1876, from the Upper Cretaceous (Upper Campanian) Bearpaw Shale and Pierre Shale of the Western Interior of North America and lower jaws of the related ammonite ...