In 1902 the Cope Collection of Fossil Reptiles was presented to the American Museum of Natural History by President Morris K. Jesup. It included all of Cope’s types and other dinosaur material of Morrison age from the vicinity of Canyon City, Colorado. Several of these types antedated in definition Marsh’s types from beds of similar age. Cope’s references were full, but accompanied by few figures; Marsh’s came later and were adequately illustrated. Marsh also issued, in the publications of the United States Geological Survey, two more or less complete summaries of the characters of these animals, which were fully illustrated and widely distributed; consequently they became well established in the literature, while Cope’s are still unrecognized and imperfectly known. Our object has been to describe and determine as fully as possible Cope’s types, especially of the Opisthoccelia, the most important of which is that of Camarasaurus. This generic name antedates . . .