Among the many reptiles of the past which have sought a more congenial or a safer home in the water few have had a more interesting history, or a briefer one, than those to which the late Professor Cope gave the name Choristodera in 1876. Many students of repute consider the group an order, others a suborder of the Rhynchocephalia. The group, whether order or suborder, are interesting because of their long and devious migrations from western North America to Europe, or vice versa, through rivers and ponds; interesting also because of the persistence of certain old-fashioned traits that clung to them long after their disappearance in other animals. Perhaps these traits were among the causes of their merely moderate success as animals of the water, traits that led to their early dissolution. Like the proganosaurs, which they must have resembled in external appearance not a little, they wandered from their birthplace in the western continent, to perish in the eastern; and like them their span of existence was short. Their history among mankind, too, is brief. The first known specimens, from western North America, were described by Professor Cope in 1876, under the name _Champsosaurus_. In the following year Professor Gervais of Paris made known another form from Rheims, which he called _Simoedosaurus_, so closely allied to the American that even yet they have not been sharply distinguished. Some years later these European specimens were more fully described by the well-known Belgian paleontologist, Dr. Dollo, but it has been only within the past few years that our knowledge of the animals has been made at all complete by the discovery and description of several excellent skeletons of _Champsosaurus_ by Mr. Barnum Brown of New York. [Illustration: FIG. 87.—_Champsosaurus_; skeleton, as mounted in American Museum. (Brown.)]